Best way to get a campground reservation in Yosemite Valley?

I am planning a trip to Yosemite during this summer in the months of either June, July or August. I was wondering if anyone has ever been through the process of making reservations, and if you have been successful, I would LOVE to know how you went about that.

Also, do you have any tips on which place would be the most ideal in terms of proximity to good/intermidiate hiking trails??