1. Quality hoses that are the proper diameter, length and thickness of material.
Silicone lined, reinforced with multiple plies of Nomex - poor quality or misapplied hoses grow in diameter and shorten under pressure. They can't take the heat, and soften.
Not too thin - thin hoses are flimsy.
Not too short - short hoses are the number one cause of dents to the underside of your hood.
2. Quality hose clamps.
Breeze Heavy Duty Large Spring Spring-Loaded T-Bolts - B9224 - these are killer clamps, absolutely the best I've come by.
3. Taking the time to line things up.
All systems have slop. Make sure it works for you, not against you.
4. Make sure that the hoses are fully over the beads of the turbo, tubes, and intercooler.
Again, are your hoses long enough, or are you kidding yourself?
5. Everything scrupulously clean - turbo, hoses, clamps, tubes, intercooler, throttle body.
Brakleen
Work with clean hands and clean tools.
6. Some guys rough up the turbo, hoses, tubes, intercooler, and/or throttle body using sandpaper. I have not found the need.
7. The toughest connection is at the throttle body. The nose of the throttle body, OEM or aftermarket, is too short, shorter than the width of a standard clamp, and there is no bead. Chalk it up to piss poor engineering. As such, this hose tends to walk. Clean it and clamp it hard, using the clamp I mentioned above. Tighten the heck out of it. Check that the hose is up against the shoulder of the throttle body nose frequently. If not, correct and retighten as necessary. Bias your installation so that there is as little strain on this hose as possible.
8. Of course, staying out of boost for a day or two while your installation "takes a set" would be good, assuming you have the patience. It seems like once things "stick" they stay "stuck" until you disturb them.