This is my third season of tuna fishing. Gave up Salmon fishing in Canada this year to focus on tuna! This late season stuff is challenging compared to early season.... as I've heard it said, it's easy to catch tuna in June and July!
At any rate, at the risk of repeating what's already been said, here's my 2 cents.
Use Terrafin, Ripacharts, etc to find the water you want to fish.
Pump all your friends for coordinates.
When you get there, look for birds! Every successful trip this late season has been when we found birds. If they are sitting on the water, we troll around them. If we see jumpers or birds diving, we've has some success trolling in tighter and tighter circles until you cross the edge of the school. We start our circling a good distance away and then tighten it.
Casting to jumpers is the ultimate challenge - getting close enough without spooking them. This is something we're still learning how to do. We try to get upwind of the school, shut down the motor and start casting.
Don't be afraid to stop and fish if you like the conditions. Too many times it's easy to get focused on running to the magic spot on your GPS and you run right over fish.
Go to lighter gear on your casting "stuff". After reading Salty Dog I put together an 8' Ugly Stick (8-20 lb) with 40 lb Power Pro, small swivel with 18 inches of 30 lb leader tied directly to the swimbait (2 oz). You can cast quite a ways, and you get a great fight!
Read Salty Dog for lots of advice - I can't tell you how much I've learned from reading the threads here.
Finally, see if you can ride along with an experienced tuna captain - or invite him to fish with you on your boat. I did this earlier this year with one of our best tuna skippers. It was a real eye-opener!
Best of Luck!