To switch first, probably going to practice to switch and to reg all weekend
Can you do backside 180s? Because a frontside boardslide to switch is very much like just doing a backside 180, but with a stall in the middle as you slide across the box.
Basically the only new part is remembering to keep your base flat as you ride across the box.
If not and you're totally new to boxes and spins, I'd start by literally just standing on the box stationary in a frontside boardslide position to get used to that balance and keeping your board flat in that position (sliding with back downhill).
Obviously, don't do this if there is a huge line of people waiting to hit the box, but if you can get some alone time to quickly stand on a box a few times in that frontside boardslide position it will help you with getting used to being in that position later.
Still working on park for myself.
but a tip and known fact for me is to bend my knee more !! This forces me to pressure flat. As was pointed out by a member I need get lower and when you do this it is very easy to force that board to stay flat.
The pressure and flex in your knees, ankles and keeping that center of gravity lower all combine to help keep a flat base.
As I said I'm still perfecting this but it has helped me