I'm not the the most mechanically inclined person ever, but I recently replaced my own starter (please hold the applause), so riding that wave of accomplishment, I feel like I should take a stab at this before turning it over to a mechanic.
I have a 2001 Sahara with 120k. Recently I went away on vacation for a week, while it sat in the driveway. Up till then it always started right up, but since returning sometimes it rotates but doesn't turn over on the first and sometimes second try. It so far has always started up by the third try. Sometimes it will go for days starting fine, but then suddenly have trouble starting again. After starting it seems to run just fine. Any immediate obvious things I should check?