We've been there twice and love Glacier. We prefer to stay on the west side for awhile and then move to the east side. On the west side you can reserve beforehand at Fish Creek, and it's a great and huge campground. I strongly recommend loop D, which has the lake on one side and a nice rushing creek by almost all the sites on the other side. It seems to be a little less crowded than the other loops. I had a hard time learning this but there are free showers in loop A, which is an easy walk through the woods from D. There are only 2 showers but we had hot water with no wait late at night, maybe 10ish. Also, if you have bikes, you can ride along the road and then hit a trail by some private cabins over to Apgar Village, where you'll find anything you need. When you get there, I strongly recommend driving in and parking at Apgar first anyway. The view from the shore by the boat rental will put a smile on your face whether you've just driven 5 miles or 5000. I've always wanted to stay at Apgar campground but it's been full and we haven't even driven through it.
Any campground without a reservation system is going to fill up by mid morning usually, so plan your daily activities accordingly. We like our routine of reserving first at Fish Creek so we can wind down and think about what we want to do for a day or two. Last time, on our last day there, we woke up early and drove over Logan pass to the Many Glacier side and were able to get a site even though we got there late, about noon. I recommend a little earlier. Just pass everything after the pass, go get your site, and come back if you choose this route. By the time we got over to Many Glacier though, there was so much to do there we didn't go back. The hikes out of Many Glacier are among the best I've ever seen. There is a LOT of bear activity on this side though, be prepared and careful. Also, there are pay showers back behind the store at Many Glacier. They are a little harder to find than most, located squarely in the middle of the employee cabins.
On our first visit to Glacier we got a room Glacier Park Lodge in East Glacier, the night before we headed home. It was expensive but pretty amazing.
A pretty abbreviated glimpse of our latest trip is here:
I thought I had lots more pics of our first trip but I guess that was before I started posting trip reports here.
I'm glad to get more in depth if you need.