Make sure you are using a quality roller frame and sleeve. Cheap frames don't roll smoothly and tend to squeeze paint out of the sleeve. I prefer the Wooster brand but also use Purdy brand but you may find one that works better than another for you. Take a few minutes to “tack off” a new roller by using the sticky side of a little masking tape to get the fuzz of the new roller. I find a well cared for used roller works better for me than a new one. It seems like it takes a couple of gallons of paint to break a new one in. Make sure to clean them out well at the end of the day and keep them in plastic bags when taking a break while painting. Buy a roller scraper to make the cleaning job a little easier. If you paint a lot make a spinner from an old roller frame that goes in your drill and spin them out in a laundry tray or 5 gal bucket.