As a general rule, 3betting ~3x in position and ~3.5-4x oop is the standard, but it can definitely be deviated from.
This is one of those subjects that a million books could be written on, so I'll try to give general points. For ex, some factors that should affect your size:
-position. Bigger OOP, smaller IP.
-stack size. Smaller stack size = smaller 3bet, deeper = bigger 3bet usually.
-the size of the open, and/or the number of calls in between. Like in a squeeze spot where you get a 3x open and a flat, I usually bump to 13-15bbs or so as opposed to my usual 9-12bbs without the call in the middle. Similarly I usually 3bet bigger when the open is to 4x or 5x,
but if my opponent simply opens big and folds well to 3bets, we can still stick with a smaller size since he often will still be folding with the same frequency, so the smaller bet saves us some money.
-opponent's tendencies. Similar to above, if villain opens frequently and folds really well to 3bets, I try to find the smallest I can 3bet without it changing his range. Usually that means getting down to 3x IP and OOP. Any smaller than that and people start doing weird things like calling with 97o and stuff. As a kind of contrast to that, if he flats lots of 3bets but gives up really easily postflop, I tend to open big PF and cbet small postflop. I could go on with other examples, but basically you're looking to find the leak in your opponent's game, and exploit it with similar tactics.
-the strength of villain's open range. This kind of affects how
often I'm 3betting more than my 3bet
size, but it's important. Like if a 16/12 nit opens UTG and it folds to me with AA in the BB, I'm just 3betting to 15bbs or something.
I'm guessing you're somewhere below 50nl, right? If that's the case I really don't think you should worry about 4bet
bluffing yet. Just concentrate on figuring out how wide you can
value 4bet, and do so. I say that because I don't think people at those stakes 3bet wide enough to be able to fold once 4bet, so it's just going to be spewing money.
But ya, as I said 3betting frequency and 3bet sizing is very situational and can depend on a lot of things (including a bunch of things I'm sure I forgot). As a general rule with full stacks, 3x IP and 4x OOP and something like a pot sized raise in squeeze spots is fine.
