In "Harrington on Holdem", Dan writes that Continuation Bets (When you didnt hit the flop, but want to represent a strong hand) should be fairly bigger than "Probe Bets" (When you want to test what your opponent is holding)
First, a continuation bet is when YOU were the AGRESSOR preflop and everybody checked to you. A probe bet is when the preflop-agressor (NOT you) checks to you. So you want to find out where you are.
For continuation bets, he writes that you should bet around half the pot to pot-size. Just to chase anyone with weaker hands out, and dont give them the right odds
if they want to draw.
For probe bets, a little less than half the pot.. Because you can easier let it go when you got check-raised and didnt invest that much. And you dont commit yourself to the pot.
gl with trying!!