As above. Rather play a move that you understand than a move that you think will impress.
Solid, direct moves are your best bet. Don't dither about. Your stronger opponent will just continually improve his position until the inevitable attack. (But do play within your capabilities. An attack needs more than one or two pieces!)
Find a plan (eg. kingside attack, queenside play, play in the centre) and stick to it. Will you play with pieces, pawns, or a combination?
Analyse every position and only make a move when you're happy that it will not lead to a disadvantage.
Play the opening that you know best.
Play shorter time controls but put in more analysis than your normal games.
Make moves that are flexible: do more than one thing.
Remember to centralise your pieces.
Don't make any tactical errors and watch your opponent sweat!
[Event "January 2010 Sprint Duel 64 III"]
[Site "http://www.redhotpawn.com"]
[Date "2010.06.04"]
[EndDate "2010.06.24"]
[Round "4"]
[White "tcvegas"]
[Black "Green Paladin"]
[WhiteRating "1618"]
[BlackRating "1974"]
[WhiteELO "1618"]
[BlackELO "1974"]
[Result "1-0"]
[GameId "7491424"]
1. d4 Ng8f6 2. e3 g6 3. Bf1d3 Bf8g7 4. f4 d6 5. Ng1f3 O-O 6. O-O Bc8g4
7. Nb1d2 Nb8d7 8. Qd1e1 c5 9. c3 a6 10. Nf3h4 b5 11. f5 c4 12. Bd3c2 g5
13. Nh4f3 h6 14. e4 Bg4xf3 15. Nd2xf3 Rf8e8 16. Qe1g3 Nf6h7 17. h4 f6
18. hxg5 fxg5 19. Kg1f2 Nd7f6 20. Rf1h1 e6 21. e5 dxe5 22. dxe5 exf5
23. exf6 Qd8xf6 24. Nf3d4 Ra8d8 25. Rh1d1 b4 26. Qg3f3 bxc3 27. bxc3 Qf6b6
28. Ra1b1 Qb6c5 29. a4 g4 30. Qf3f4 Nh7g5 31. Kf2g1 Re8e2 32. Bc2xf5 Bg7xd4
33. cxd4 g3 34. Rb1b8 Re2e8 35. Bf5e6 Ng5xe6 36. Rb8xd8 Qc5h5 37. Rd8xe8 Kg8h7 38. Qf4e4 1-0