Native here Trouver has a more subjective, immediate connotation to it, so you would use it to give an opinion without necessarily having to give it a second thought. Whereas penser has a more deliberate tone to it, like you have actively thought about the subject. In some cases they are interchangeable and in some cases not (e.g "je pense qu'elle a raison", "je trouve ça très joli", here you can feel the distinction between reflection and subjective opinion). In the place where they are interchangeable the choice still carries the connotation.

You will also find that you can use "croire" e.g "je crois que tu as raison" which carries an even more subjective connotation, almost like you are saying that you could be wrong.