online tourneys

[Eskon]

I have just started to get into online tourneys and have a few questions:

1.Is it ever OK to go allin preflop?and if so...when? I have tried a few times in some of the Free roll touneys and generally lose.(AA or KK when I do and end up losing to somthing that shouldnt even be played)

2.Is it better to be more aggressive early or later(or does it really matter)I mix up my play alot depending on the table but generrally find that when the BB gets to 1K I am gennerally on the short stack due to the cost to see the flop (which seems to disagree with me most of the time,even with a good starting hand)

I see myself as an OK player(nothing to special)

Best finish: 33 out of 800
worst finish: 370 out of 800 (due to allin with AA.lost to 72 off)
generally place between 80 to 140 out of 800

Also new to this forum,so if this is the wrong place let me know.