This is a good thread to get all the complications and exceptions posted!

"Жать - жну... эээ... жму... эээ..." Lipson shows the stem for this as simply жм+ , seems like it follows all the rules to get past and infinitive.

Even жечь seems to follow the rules. жг+ with spelling rule (can't have жгё, shift to жжё) and other things to get present, past, infinitive, etc. Doesn't seem very exceptional.

I'll try to get the rules copied here so you can see them. Seems like for almost all verbs, one stem allows complete conjugation by following rules. This seems to be intermediate or advanced, not for beginners.

The book I'm using is Alexander Lipson, A Russian Course, 1981 ed.