There are a number of ways to prevent this. Many use wax on the bushings, others have soaked them in "break free" a gun lubricant with teflon in it.
I use medium CA and rub it on in 3 to 4 thin coats. After drying each coat I simply loosen the nut and break the bushings loose, then go to the next coat.
It is a little more critical when using bushings other than 7mm, that fit inside the tube. They can be hard to break loose if you go nuts with the CA.
To start out I would recomend using paste wax on the bushings before you start.