I've been getting away with a basic, rather sub-par (IMO) 3bet defense game given generally poorly constructed 3betting ranges from the pool. But I have moved up stakes recently and can immediately see that players have a much better, well balanced 3betting game and even 4betting. Getting 3bet still makes me uncomfortable, unsure of correct line (4bet bluff?, 4bet for value but good enough to call 5bet?, just fold or call?, etc), especially OP.

What do you think is the best method to go about strengthening my 3bet defense game?

Thanks everyone.