1) Seam Seal.. Everything.
A little preparation can go a long way, if your gear isn't seam sealed start there.
There are two ways to seam seal, brush on sealant from the outside (typically with a silicone based sealant, with silicone coated fabric) or heat weld seam tape (trickier to do yourself).
2) Setup Priority.
When you arrive to your camp site in the rain the order you set up camp in could mean you are dry as a bone or miserable. Setup your rain protection FIRST, if you are hammock camping set up your rain fly or air tent. If you are ground camping set up your poles on your footprint and then add the rain fly (if possible). With your rain shelter in place you can unpack the rest of your gear while being completely dry.
Pro Tip: Keep your Rain Fly or Shelter at the top of your pack or on the outside, so it's easily accessible WITHOUT pulling all your other gear out.
3) Take the High Ground.
If you are ground camping this is crazy important. Pay attention to the grade of your campsite, setting up in a low spot or a flat spot could equal a flooded tent. Try to position yourself on a slight slope or at least create a trenched exit for the water to flow towards.
Air campers have a much easier time here, since you are elevated you don't have to worry about your shelter flooding out. You can even setup on a slope so you aren't stepping into a mud puddle when you exit your Air Camp.
Pro Tip: Don't forget about where your pack is during a storm, a wet and muddy pack equals a terrible trail day not to mention ruined gear.
4) Is Your Fabric Waterproof?
Most shelters aren't actually "Waterproof" they are "Water resistant", which means water will bead up and roll off - to a point. The reality is you want your rainfly to withstand a water column of pressure, not just bead up and roll off. High end rain fly's and shelters generally use coatings for waterproofing fabric, the typical looks like this: DWR exterior and a Polyurethane interior (with a waterproof rating). Some people go a step further and apply silicone coatings to the exterior. The minimum water column for a rain fly should be 1200mm.
Pro Tip: If you find out your fabric isn't waterproof, make it through your trip by wiping the fabric down with "Never Wet". Next thing to do is upgrade.
5) Air Campers Pay Attention to your Suspension.
The MOST vulnerable area of any hammock are the connection ends, more specifically the suspension connecting the hammock to the tree. What generally happens is water will collect on your suspension line and then run down that line to your hammock, ultimately soaking you and your insulation. To avoid this you need to create a 'water break' on your suspension. Some people tie shoe laces on their lines to help with this. We opted to incorporate suspension protection into our shelter designs.