In 35912... it looks like Italy was after you from the beginning, so your Hedgehog move was slick, I can't fault you for that. I would advise opening to Serbia, not Rumania, though. Rumania can be secured by any Russia that opens Mos -> Ukr in that case (as the tendency around here seems to be) even if they don't stand you out, and honestly you're probably going to see a fleet there as often as an army. A Russian fleet in Rumania is nothing to fear. Meanwhile, Serbia can't be forced by any other power. That opening will guarantee you a build.
Diplomatically, I don't think you could have done much. There was a Juggernaut on the cards, and Italian players that don't prop up Austria tend to be next. It might have been your saving grace, though, since Turkey stabbed Russia, probably due to you being preoccupied and supposedly easy pickings later.
Your defense against Italy was admirable and the right play; aside from Bud -> Rum, I don't think you could have improved. You just have those games sometime. I'm in an anon as England, and I turned down an offer from France to be game-long allies on principle (it was in S1901, like hell I'm committing to that!)... next thing you know there's a Sealion on the books.
19811 was simple enough. Your RA collapsed against you. I don't blame that one on you very much. Italy attacked at the right time, but you countered magnificently, I don't think he got a single center off you once! The problem was that you had tactically and strategically bereft French play (typical Frenchies ;]), and with Turkey dead, no one could deliver the coup de grace to Italy, forcing you on defense until Russia made his late push on you. The Russian was also bad strategically, ignoring the greater English threat until it was far too late. Again, nothing you really could have done differently; your downfall was due to bad play by other countries.
17552... sorry if this sounds like a jackass comment, but I have no fucking clue what you were doing with your opening. It looked to me as though you had a DMZ in the Black Sea, but intended to attack Russia anyway, so you went to Armenia... but if so, you might as well have full-on stabbed and taken the Black Sea in S1901. Then you'd have had a shot at holding out. Your position just caved in because you angered MadMarx without actually injuring him in any appreciable way. Not a smart play. ;P Austria and Italy were pretty determined against you as well, but if you hadn't angered Russia I think you could have held them off.
13682 looked fine to me, though I suspect the inconsistent French player had to do with that. You were facing an EF after 1902 and that is always troublesome. Luckily you and England recognized the Austro-Italian threat and acted accordingly, carving up an inconsistent French player in time to get a draw.
That's the best I can figure from just moves. I hope it helps, though without being privy to press I can't guarantee I got the all-important diplomatic phase down.
As for more general pointers, the early game is all about diplomacy. I generally try not to lie to other players in the early going, but it is prudent to be generous with other players' centers. An England willing to offer the French homeland and Belgium to Germany in exchange for being allowed Scandinavia and Iberia is far better off than one who leaves his options over for the mainland, even if he has no intention of staying out of the French homeland spoils. Think of the early game as an auction: unless you, your competitor, and the seller can come to some agreement ahead of time on how to divvy up the prize (as in, for instance, a Western Triple), you have to outbid your competitor to get the prize.
And you better move fast. The other critical part of earlygame negotiations is something called "controlling the document." I think that's the name, surely an attorney-at-lawlz can help me out, for being the one to propose deals from the get-go. The player which proposes first gains a huge psychological advantage in future negotiations, as this player is seen as the leader. It is his plans which are more often followed and his stabs, then, that are more successful.
The fact that you were in game 17552 with such a star-studded cast tells me you've probably heard this before. You seem like a pretty good player. You probably just ended up unlucky in a few of those games. Believe it or not, luck DOES play a role in Diplomacy. It's not pure CHANCE, like a dice roll, but sometimes you just don't get the breaks you need. You're probably just hitting a rough stretch. I get 'em on occasions and it sucks. The best thing you can do is work to break an alliance. And given how long I've rambled, and my complete failure to achieve this in recent games (see http://webdiplomacy.net/board.php?
gameID=37205#gamePanel for a prime example of my brilliant rival Indybroughton and his ally Dalemark refusing to buy the "I'll throw my centers" line -- if they won't buy that you're truly cooked), that subject is best saved for someone else.