Adequately seal joints to keep moisture from infiltrating where it can damage sheathing and the back of siding.
Keeping moisture from infiltrating where it can damage sheathing and the back of siding is relatively simple. The usual problems are inadequate or poorly installed caulking around windows, doors, gable trims, and other joints. Take the time to inspect all the places where water could get in and apply high-quality caulk where needed. The exception is vinyl siding, which should be caulked only in those places where vinyl pieces abut wood or metal surfaces.
Also check your home's flashings. Check whether you have flashings where they are needed--above doors and windows, at vertical joints of panel or board-and-batten siding, and at the top of a water table. If you are missing some flashings, consult with a professional to see if you should remove siding pieces to install flashing or if you should simply caulk the joint well.
An hour or two to replace damaged flashing or apply caulk around several windows or doors
Caulking gun, tin snips, lineman's pliers, flat pry bar, hammer
Caulking, a skill that you can learn with 15 minutes or so of practice
Inspect around windows, doors, and trim boards to see if you need to replace flashings or apply caulk.
High-quality exterior caulk, flashings as needed, nails
Practice on scrap pieces if you are unsure of your skills. Hold the tube's tip against the joint, squeeze the gun's trigger, and start moving downward once caulk starts to come out. Aim for smooth motions, continually squeezing the trigger to produce smooth lines. When you get to the end, unhook the lever to stop the flow.
Some people prefer to smooth caulk lines using a tool made for the purpose. Several tools are available. A tightly wadded rag (above) dampened with water (for latex or acrylic caulk) or mineral spirits (for oil-base caulk) is one option. You'l need to periodically rewad and clean the rag.