Depends on the game I guess. If the story's interesting, I'll usually just rush through to the end and ignore most of the side quests. If I'm not bored by the time I finish, I might go back to do some of the side quests or do them on another playthrough (I'll wait a few weeks or months first).
If the story's not that interesting, I might get bored part way through and take a break for a week or two. I almost always come back to finish them though.
I actually don't play a whole lot of RPGs though. I'm not a huge fan of turn based combat unless it's Pokemon, so I usually only play them for the story.