Obviously the bet size depends on a lot of things. With AJ on a flop of J83 rainbow it's enough to bet half pot because no hand will have anywhere near odds to draw and you want to get money from worse hands and not bloat the pot to a size where you'll only get called when you're beaten.
With JT6 and two of a suit you need to bet bigger because all kinds of draws are out. With JJA you once again can make the bet smaller because most likely your opponent is drawing dead. With more opponents you need to bet bigger, with fewer you can bet smaller.
My "standard" bet is usually 80-100% of the pot on the flop, and slightly smaller on the turn. But these are usually when the pot is raised. If the pot is unraised with a lot of players and I have a big hand, like 66 on a board of A65 and there is a flush draw, I will usually overbet the pot substantially because although the bet is improportional to the pot, it won't have to be huge.
NL $50
6 people limp into the pot, flop comes
and I hold 66. There is $3 in the pot, but I might very well bet $4 or $5 because that's not a very large bet to people, if I had raised 4xBB and gotten 2 callers the pot would have been $6 and I would have bet $5 most of the time, so people will have seen me bet that amount before and think it is just a normal bet, not realising they are getting awful odds to draw or call with their Ace. Also, if someone has a decent Ace or two-pair and decide to raise, the big size of my bet will allow me to get my stack in by the river.