85% of my fishing here in S. Florida is around docks so I feel pretty confident with my skills.
A lot of good information has been given so far, but I'd like to summarize by pointing out a few key pieces of advice.
1. BrianinMD pointed out to make sure you fish the WHOLE dock, especially the back. I can't count high enough on how many anglers I see fishing a dock but NEVER fish the back. BIG mistake. Don't just skip your bait from the front to the back, but also position your boat next to the shore and flip/toss/pitch/skip or do whatever it takes to cast underneath the dock parralell to shore.
2. Make more than a couple casts around the dock. Sometimes it will take half a dozen tosses to the same pylon or boat lift to entice the fish into biting.
3. Use the trolling motor as little as possible.
4. Don't discount the outer peremiter of the dock. Fish every cast, even the ones that accidently hit the edge of the dock instead of going all the way underneath. I have caught A LOT of bass on goofed up casts.
5. FishinDaddy pointed out to use cranks. Absolutely true. Many people wil throw plastics/jigs an nothing else. Change it up. I will throw 3-4 different baits at the same dock before moving to the next
Here's what I do if there are several docks in a row. I usually start out throwing a Senko (just because). If I get no hits or fish after fishing the entire dock then I will throw a crankbait and then a spinnerbait. I will let the spinnerbait sink to the bottom and simply bounce it off the bottom or slow roll it, dragging the bottom. If still no hits, then I move to the next dock and repeat the process.
My other way of doing this is I'll fish the same bait at three to five docks in a row. If no hits or fish, then I'll go back to the first dock and throw a cranckbait, moving from dock to dock. When I get to the last dock, I start over again at the firs dock with the spinnerbait.
6. If there are two of us in the boat fishing the docks, then I make sure the guy in the back is throwing a different bait then me until we find what the fish want.
These are just a few key things that I do fishing docks but don't limit yourself to just them.
Sam and I hit the aENTER button at the same time so I didn't see his post until after I typed mine, but he made some very good points too.