I just recently finished my first Guillow's kit at the tender young age of 38. You'll want to use straight dope to brush onto the airframe to provide a smooth, even surface for the tissue to adhere to. When you actually attach the tissue to the air frame, you can either use more straight dope, or use plain old white school glue thinned with a bit of warm water.

The dope dries up very quickly, so it can be difficult to get larger pieces of tissue pressed down properly without getting loose spots on the covering. The thinned white glue sticks much better, but if it pools up in the joints it can get the tissue too wet and it will shred.

One the basic tissue covering is applied to the air frame, you will gently spray it all over with a light misting of water. When the water evaporates, it will gently shrink and tighten up the tissue covering. After you have the tissue tightened up via this method, you then go over all of the covering with a 50% dope and 50% dope thinner mixture. This coating will continue to shrink the covering ever so slightly while adding strength to the covering. This is also a good time to be applying color by using colored dope with thinner.

Make sure you do all of this in a well ventilated area, or 5 minutes after you open the cap on the dope bottle you'll be imagining that your furniture is talking to you.

Good luck and good building!