How to make suggestions to professors on how to teach?
It depends on what your goal is.

If you have a particular course and a particular professor, and you want to see changes before the course ends, you may need some political power or not.  Many professors appreciate feedback, some don't, and you can usually tell by noting which ones ask for it.  If they do ask, follow their format for giving feedback, and add a note saying that you have more specific suggestions if they wish to discuss it further.  If they don't, you will either have to drop it or try a different tactic.

If the course has teaching assistants, you can usually give some feedback through them, although to promote understanding, you might give them a copy in writing to hand to the professor.  If there are none, you may have to submit feedback through the department; there usually are people in that department in charge of the quality of teaching, and they can advise you at least as well as on this forum.

If the issue is more with a person than a situation, then I recommend getting advice from colleagues of that person on how to make such an approach.  Through the department is likely the best way, but it highly depends on the situation.

If the issue is more with a class structure than a person, you can make suggestions, but they will likely be referred to the next class.

The applicability of all of the above is subject to class size, level of instruction, and many other factors.  Without more specifics, I imagine your best answer in the long run is by using official channels.  That way if anything goes wrong, the process can be blamed and not you.