I had the same doubts. Here are my thoughts about this issue. There are three most important factors: board, number of opponents, was the pot raised preflop or not.
The board structure is an obvious thing, suitedness, connectiveness. I would say that 2 suited rag board with no connectiveness is not very drawy against one opponent and I would often bet standard 2/3rd pot for value. While 2 suited board with a J and T against 2 opponents I would consider very drawy and bet it about pot, even more than a pot sometimes against very loose opponents (it's likely that one of them has a draw or a pair which is also a kind of draw).
The last thing is the question if the pot was raised or not preflop. If it was raised, I don't care as much about small card connectiveness, although I wouldn't ignore this completely. I'm very aware of mid - high cards: 8,9,T,J,Q, both in raised and not raised pot, people loves to limp them and don't give up drawing hands easily.
One more thing. I do this mistake quite often. I bet/raise high for protection and than when the draw completes and opponent bets into me I can't fold. It's important to remember that when u bet or raise for protection u have to be ready to give up the hand, if u are not the whole protection is useless because u give him good implied odds that cover the protection loses.
