Sonic is a well-designed character (thanks P:M devs) so while there are guaranteed followups you can practice it's better to just be fluent w/ your many movement options and to remember what works generally against fast fallers, floaties, etc. Just the tip of the iceberg:
You have three primary options for movement: running/dash dancing, side-b, and down-b (and wavedashing, but you can't wavedash out of down-b anymore):
1) Sonic has the fastest run speed, and probably the best dash dance game
2) Side-b bounces if you hold b, floors otherwise and you can jump cancel it into a wavedash, grab, aerial, blast attack, etc. as well as hit a to do a slide kick; can also be ledge cancelled, so you can weave around platforms quickly i.e. Yoshi's, Battlefield, etc. or cancel off the ledge into blast/homing attack, aerial, etc. Also you can run off the ledge and side-b back towards it and HOLD b to grab ledge quickly
3) Down-b charge can be stopped in place/while moving by hitting l; if you get a hit confirm w/ the spin attack you can do a turnaround or jump to activate another hitbox (correct me if I'm wrong here not entirely sure how this mechanic works). After you jump you'll do a full hop and you can aerial, blast attack, etc. to continue your combo from there. You can also spin shot by hitting jump immediately after down-b and do a quick 45 degree leap that uses a jump (your best recovery option from afar, given you have your second jump)
There are a lot more advanced techs, matchup-specific combos, etc. I can delve into, but your best bet is to 1) read the hitbox/frame data thread and 2) watch videos of the best i.e. Wizzrobe, Darky, etc. (make sure it's P:M 3.0 though, Sonic was a different beast before)
Feel free to ask me anything specific (i.e. recovery, matchups, etc.) and I'll go into more detail if I can. I don't know everything but I'm pretty familiar w/ the most common matchups (i.e. spacies, Marth, etc.)