The first tip is to buy your parts here and have your mechanic install them. Installing an exhaust can be a trying experience if you do not have a lift so you might want to consider this.
PB Blaster is a great penetrating oil product for making tough nuts come off without heat. Much better than WD-40.
Use anti-seize on exhaust manifold bolts so that they can be removed when the time comes.
Aluminized or stainless exhausts will last much longer.
If you make a lot of short trips your exhaust system may not last as long as it should as it will not get hot enough to evaporate all the moisture in the system.
