@peterwiggin: allow me to shamelessly quote myself :)
"If you're not the guy in the driver's seat, your role is to break up alliances that are against you and to continuously read the board and convince others that they need to target someone else to either prevent a solo, prevent a personal threat by getting others to personalize that threat as well, and to find your footing and growth to change the course of events that are not unfolding in your favor. "
A few examples of this are as follows:
--Early game: let's assume you're the odd man out and are facing a fight alone against an alliance. Assume you're England in the Germany/France alliance example. You need to work at breaking up the alliance. Here are a few examples:
1) in the Spring and Fall as alliances are forming and you aren't necessarily the "losing" force, you work to establish checks and balances. If I'm England, part of my press is sometimes (but not always or even a majority of the time) befriending Russia and/or Italy. If I can talk to them and get on their good side, in the event of a FG alliance, I may be able to convince Italy to push into France or Russia to push into Germany. You do this by offering them something in return. This allows you to have an ally in case things go sour.
2) If you can't (or don't) get the checks and balances guy to work with you and you find yourself in a perilous situation, you simply try to get someone to see your downfall as bad for their success. If I'm England and I'm going to be losing, Italy, Russia and sometimes Austria are my go-to guys. You have to paint a picture to them that gets them to believe that when you die, France and Germany are coming for them as their next target. You have to make it believable but you also have to offer an alternative. It's not enough to simply say "hey man, if you don't help me, you're the next to die". Most players don't buy into that sort of empty scare tactic because at the present, there's no evidence to support your claim. If you say "hey man, I need your help. If I die, you could be the next target. The only way to prevent that is to send even one unit to my aid. If you do, I will make it worth your while. I'm not looking for growth, but you are. If you can send even 1 unit my way, I can give it support into my enemy's nearby center(s)." This approach has both believability and something to offer. Even if the person you're talking to doesn't buy into your doom and gloom story, they will at least consider your offer because they stand to benefit. A note on this: YOU have to be the one to put the plan together. You can't count on someone else to come up with a plan to rescue you (and you shouldn't expect it, either). Some players (myself included) are often interested in helping a weak guy because they offer things without really asking much in return. I tend to like allies like this because of what they offer. Sometimes, I'm the guy that offers to help a weakened player in exchange for something profitable. (See my midgame segment below).
Midgame: If you're the losing party in the midgame, strategy depends on your scenario. Let's assume that you're Germany in the midgame and after defeating England, France decides his best means of moving toward the solo is to plow straight through you. You bought into his ruse to turn and fight Russia only to be knifed in the back. This is the part where keeping up a positive relationship with the east (or west if you're part of the east) is extremely beneficial. At this stage, you work to paint a picture to others of a very strong and dominating France that is looking to solo. You need the help, and if it doesn't come soon, France will be out of control. Again, this needs to be both (a) believable, and (b) carry some sort of reward. If France is genuinely a strong solo threat (even if he hasn't moved into a solo-possible position yet), others will see it and the reward is stopping the solo. This tends to take place in the endgame more than the midgame for obvious reasons. Therefore, you need to offer incentive for others to stick their necks out and help you. This offer is much easier to make because both spheres are condensing, alliances are shifting, and players are looking to other areas to make gains, so why not accept your offer to push into your sphere and take centers with your support? The drawback is that it carries risk. Anytime you're inviting someone over to play, you're opening up a player to become a possible solo threat by crossing the stalemate line. Second, and equally important is the possibility that they come to your aid only to side with your enemy and knife you further. Again, checks and balances comes into play. Always try to have a backup plan. This can't always happen, but you need to always *try* to make it happen. Simply allowing the game to go its own course only means you'll lose. You have to have the mindset that your position won't change unless you actively work to make it change. Keep talking, keep moving and keep making deals.
One example of this is a game I played recently where I was Germany. I got screwed early on by a EF alliance that I didn't think was on the map. I requested Russian aid and quickly found myself fighting 3 countries. At each season, I made offers to players and they would accept only to betray me again. I knew I was probably being duped each time I made an offer, but it had to be done. If I quit talking and quit proposing plans, then my game ends at that point, even while I have units on the map. I spent the remaining few years in the game offering myself to anyone that would have me. In the end, I had to settle to giving France everything I had just to screw England who, in my mind, betrayed me the most when he could have gained far more by working with me. I lost, and years later France soloed. It's not a happy ending, no, but not all of them are. It's times like these when things continuously go from bad to worse that you have to keep playing. I believe that THIS is what defines a Diplomacy player. The guy that can play to the very end. It doesn't mean that I didn't get pissed off and wish that this was a FtF game so I could punch someone in the gut (would never happen but it's nice to picture :), but I have to get pissed, take a step back, turn the game off for a few hours, collect myself and approach the situation from a different, more calm attitude.
Look at the board from the standpoint of other players. What would they want that you can offer? If you're them, would your deal be worth changing course? Back again to your shoes: Can you reasonably offer what you're offering or is it just blowing smoke up someone's butt? If you make an offer, what are the chances that things will instead get worse? What other offers can be put on the table?
For this reason, I take EVERY Spring, retreat, Fall, retreat and build phase to the maximum limit. I talk to everyone. I may stop talking to someone for a while because I feel that talking to them won't be productive, won't be believed, or won't get me somewhere. Sometimes people simply need you to be silent because listening and responding might be falling into another trap.
Last, choose your words carefully. This is Diplomacy--the game of skillful negotiation. You're in hostile negotiations. The last thing you want to do is say something tongue in cheek, half hearted, cocky, belittling, or anything that could be misconstrued in such a way as to cause others to loathe you, find you irritating, or not believe you. I try to picture my press going to the other person and imagine how it would be received. There's a time for bluntness, there's a time to refuse an offer and call the other guy an idiot if he thinks that you're going to accept such a ridiculous thing. There's a time to speak volumes and a time to say half a sentence. Part of this is knowing/getting a feel for the other players and what they respond to. If you send a ton of press to people with low attention spans, they're liable to read the first sentence, last sentence and not care about anything in between. Likewise, if you write short sentences to a very detail-oriented person, they may think you don't value them or think you don't care to take the time to really put forth the effort to communicate. Getting out of a bad situation requires more work than maintaining a good one.
Endgame: Here, it's important that you make yourself indisposable. Don't be afraid to put yourself in a crappy position. You're out to stop a solo. If you're down to a handful of centers, then guarding your homeland isn't priority-one. If you reduce yourself to protecting the one or two centers you have, then you're allowing someone the opportunity to solo just to survive. The way I see it, a survival under a solo is just as crappy as a defeat when the board draws. Either way, you lose, but by not protecting your piddly centers and instead throwing yourself out there to fight the flood, you can put yourself in a valuable position for the defending team. When you do this, the defenders WANT to keep you in this game because your units and their locations are vital to THEM not losing. That's what I mean when I say you have to make YOUR loss THEIR loss. When the game is on the line, it comes down to everyone else working without regard to who stays and who goes to lock the game up. After the game gets locked up and the solo threat is diminished, players can resume looking at the board and deciding if and how to trim the fat.