Will be similar to a domestic flight.

On your FLL to SJO flight they'll distribute two landing forms - one is for immigration, the other is for customs. Don't be shocked when it asks for mother's maiden name as part of your name (it's cultural to naming in Latin America).

Departing SJO you'll first go through the primary checkpoint, I've kept my shoes on the past couple times clearing that particular checkpoint; you will have a secondary screening at the gate - no liquids past this point including water purchased inside the airport.

Upon arrival at SJO: If you need a taxi, get an official pre-paid taxi (there is an area to the left before walking out the door) -- it can be easy to miss as once you exit customs you're almost tossed straight outside .. but you can work your way back to the prepaid taxi queue.

There will be all kinds of people hawking rides - avoid them. Watch your wallet and valuables. Some area hotels do have shuttles.

Not sure where you'll be staying, but you can save time and pay your departure tax at many SJO area hotels. Otherwise, you'll need to queue to pay the departure tax at the airport.

Enjoy - Costa Rica is lovely this time of year! Pura Vida!

PS: Any particular Costa Rica Questions, feel free to send me a private message.

Edit: if weather is good, go for a window seat. You'll make a number of turns landing to avoid the mountains/volcano's and if the weather co-operates, the views can be spectacular.