Step 1: Learn 3 Balls
There is another instructable for this at https://www.instructables.com/id/EKK8HLTF11S8TQC/
. Also there is ample instruction for doing it elsewhere. It's not that hard, but make no mistake, having a 3 ball cascade pretty solid before going for the clubs is not optional.
Step 2: Play With One Club Quit a Bit
Anyhow, toss it in a full turn catching it correctly and then back and forth to between the hands. Sorta like doing one ball in the 3 ball cascade learning pattern, but get used to it a bit more - accuracy counts more then with balls. Keep it up for a while even if it looks odd - it's important to have a good feel for the club.
Step 3: Do 1 Club 2 Balls
Again, make sure you are comfortable doing this for at least a good while without missing. It will only get harder, so having it down helps.
Step 4: 2 Clubs 1 Ball
Step 5: 3 Clubs
You will start missing more, don't worry about that. There are various opinions about how to hold the two clubs, one of which will have to be thrown. Feel it out, getting the first throw pretty decent will be the hardest part if you're used to 2 clubs 1 ball. Try to grip pretty high on the clubs, below balance point but not all the way down. The first throw (and I'm reemphasizing this) is key, likely you'll lose it in the first three-four catches because you're already off balance to start with but once the pattern hits you'll keep going until you get jittery about doing it and lose it that way. Keep picking them up and restarting it. Also play with stance, one foot forward, more even, knees bent, etc - there is no single concept that works across the board but finding one for you makes a big difference.
Step 6: Done
Let me once again disclaim - I'm not very good at this. I'm just some guy who took four days or so to get this down and this is how I did it.