Categorize your opponents - Look at your opponents and study them. Watch how they play and try to categorize their play into aggressive or passive where aggressive players are those that are constantly raising or re-raising and the passive ones are those that continually just limp or call. You also need to classify them into loose or tight players where loose ones are those that play too many hands and weaker hands out of position whilst the tight ones are those that only play premium or strong hands in relation to their position. By trying to fool your opponents by varying your play you will give yourself every chance of fooling your opponents into making mistakes as they will have a hard time placing you on a hand. In essence, try and be gloriously unpredictable in the way that you play.
Check the chip stacks - You need to know exactly how large or small a stack size each of your opponents already involved in the pot is holding as well as those yet to act behind you as you will find that the biggest stacks and the tiniest stacks are more prone to call others involved in the pot. Tiny stacks call because they are getting desperate whilst the largest stacks do this as they can afford it and are looking for opportunities to bust and eliminate other players. You also need to know where the larger stacks are at your table as you need to give those players respect as they can eliminate you in a solitary hand.
What are your opponents playing? Even when you are not directly involved in a hand you should watch your opponents to try and see what kind of cards they are playing from the relative early mid and late positions as this can provide you with invaluable information later on.
Because the tables and players are constantly being broken up the turnover of players seems to be quite high in online tournaments but it will help you to make notes on your opponents against their online names. You can either do this manually in a little notebook that you can keep by the side of your computer or ideally via the note facility that exists on most if not all online sites. In this way whenever you come up against the same opponents later on in the tournament or even on another day you will have some information that may guide you to making the correct or best plays.
Re-evaluate your hand as the board develops - Learn to re-evaluate your hand as the board develops and try and back your judgment when placing your opponents on hands. With experience you will get better and better at this and just because you will get it wrong from time to time is no reason for giving up. The important thing is to be prepared to back that judgment as no limit poker is a game of fear. If you are scared of going broke then you are effectively reducing your chances of winning as absolutely nobody ever gets it right all the time. If you are prepared to stick your chips into the pot first then you are giving yourself a chance of winning.
No Limit Hold-em is a game of mistakes and the players that make the least mistakes are the ones that win. It is also a game of incomplete information so the more you have to go on against an opponent the more chance you have of making a more accurate decision.
Hopefully by following these elementary guidelines you will give yourself a chance of better success than your rivals but No-Limit Hold-em tournament poker is a very complex game and as such may take years to master. However following these types of guidelines or at least attempting to watch and categorize your opponents will be a massive step in the right direction for improving your game and giving yourself every chance of success.
Good luck to you all and hope to meet you all at the table sometime.