Question

is there a way to tell when you should use integration by parts or substitution?

Answer 1

Usually the answer to that question is dependent on the problem itself. Most of the time, you'll recognize which one to use (sometimes you'll have to do both simultaneously) but no, there is no hard and fast rule for determining which one you should choose.

Answer 2

If you use integration by parts and the integral gets more complicated than the integral you started with, try some other technique.

Answer 3

Integration by parts is often used with stuff multiplied by an exponential function. Integration comes from practice and experience, so the more you do the more you recognize what to do

Answer 4

try and learn the tabular integration by parts method as well it saves a lot of time and you are less likely to make a mistake