When you see those sweet lifted 4x4 trucks I bet your attention is running in that direction!
The first step is always the tires.
The bigger the better!
When fitting the larger tires and wheels it is almost always necessary to lift the truck. Also raised trucks are less subject to damage in situations like river crossing and rocky trails.
...keep in mind that the less you raise your truck the better you keep the original drivability and stability.
Another issue to keep in mind is the local lift laws.
Therefore lift your 4x4 truck as little as you can.
Simple step-by-step guide to a more capable 4x4! - FREE!
In my experience it is best to cut out the sheet metal from the fenders in addition to a little lift. This means you should also mount new fender flares so that the tire tread is covered from above. Thus you will avoid mud flying from the tires and in your face!
Having said that...
...you have two main methods of making your truck one of the 4x4 lifted trucks.
Body lift and suspension Lift...
Roll Over and the Center of Gravity - The traditional Jeep has a short wheelbase. Being short and light weight means that it is easy to take to places that are narrow - and a Jeep is not easily high-centered. Unfortunately the short wheelbase makes the vehicle unstable in high speed off-roading. Even taking on small obstacles can result in a bad driving rhythm. Driving steep slopes either up or down can result in a rollover backwards or forwards.
Land Rover Defender 4x4 lifting story by Skuli H. Skulason. For the Defender - 38" tires gives a good result. Here are some pictures of a modification project on a Defender. Before it was running on 35" Mud Terrain tires but is now driving on 38" Denman Ground Hawg. Pictures on the top are before modification, on the bottom is after.
4x4 Lifted Trucks!