This is something I have to deal with a lot, because I am much more introverted than most of my friends. I got over my nervousness about being direct/honest with them by imagining what it would be like if the roles were switched. If I wanted to hang out more often than another friend did, I would be totally okay with it if they told me "You know, my 'social battery' runs down really easily, so I generally need more time between hang-out sessions. Don't take it personally, it's just how I am!"
It's so much worse if you realize after the fact that someone has been spending time with you even when they didn't want to, just in order to avoid conflict. Trust me, if they're a respectful person they will immediately understand and appreciate your honesty.
A good technique is also to casually bring up your own personality needs in conversation with them, like saying "Man, work has been so exhausting lately, all I want to do on weeknights is just come home and crash, you know what I mean?" If you present it as if it's obvious and you're expecting them to agree, they probably won't feel too offended.