At least 3 months before go to
https://dtops.cbp.dhs.gov/ and apply for your customs decal. If you do not receive it in time, print out the receipt and carry it with you.
At least 2 weeks before go to CaribbeanFlyingAdventures.com and get your Cuban overflight permit.
Download the ICAO flight plan form and work out your IFR route from KEYW or X51 or KFLL to MWCR. Enter your Cuban permit number in the Remarks section
(You must file IFR).
File your IFR flight plan
Before you depart, better to activate your flight plan on the ground - it is sometimes hard to reach Miami Center and you will be at the ADIZ before you know it
Set your altimeter to 29.92 when you enter Cuban airspace (probably at IKBIX or TADPO intersections). Be aware that Cuban ATC may give you the altimeter in millibars - don?t be fazed by this, you will be out of their airspace in no time
When you land at MWCR (Grand Cayman), the tower will direct you to the FBO
The admin office is behind the FBO - you pay your fees there and file your flight plan to MWCL (Little Cayman) as well
Not as complicated as the above sounds. Have done this more than a few times (and recently)
Have fun,