I like to get all my chips in when i think i have the best hand as a general rule,there are exceptions but i think as a "newbie" you should try and master "Pure Poker" before you try and expand your game to the next level. Here's a couple of examples (to confuse you no doubt!):
Lets say we are at the 10th hand in a $5 NL rebuy tourney, you've not really been at the table long enough to get a good "feel" of the players. Your on the button and there is 2 calls of the BB in front of you. You have AK and you raise 4 times the BB, the SB folds and the BB goes all-in and has you covered. I'd call in a flash. If he has AA or KK good luck to him, if he has AK you'll probably split the pot. If he has AQ,AJ,A10 or a middle pair (most likely, either that or making a move to steal) then your at worse a 50/50 and at best dominating him. You either double up or re-buy.
Now lets say the same tourney is at the final table, say 6 left. You're on the button again and the blinds are big. same thing happens. This time i would use whatever i had learnt about the BB's previous plays, and also consider the play of the callers (they may be prone to limping in with monsters). If i put him on AQ or less i'd call, if he had an upper middle pair i would seriously consider folding, if one of the callers is short stacked i might also consider folding if i knew he was going to get a call, after all its must harder to catch when there are 2 or 3 other players in. At this point you can justify saving your chips for a better spot.
Hope this helps, and don't forget that we all have differant styles, you need to find your own by trial and error.
Good Luck.