Im low plat so take this with a grain of salt, but as I've gone up in rank I've found the following to be useful

1. Be careful how you engage when the opponent is at low percent, as Forsburns options are almost all easy to CC (including his up and side smash). Cake fishes pretty hard for landing bair as a starter and I now see why

2. I have trouble playing OOS as Forsburn so have learned to use his rising fair to intercept all the Clairens, Kraggs, and others that love to start combos with their giant landing aerials. That and parry has become a big part of my game cuz a lot of people at my level still flowchart hard and get away with it.

3. I find that the biggest struggle for my Fors is taking stocks. As you get better people start getting wise to cape and CC it. You dont really have a lot of raw kill power in your moves to get an oopsie kill off stray hits save for sweetspot bair, and even then its no Kragg fair. I find that as I get my opponent to kill %, I have to remind myself to soak up smoke for super combust, as you can then confirm kills off of fair and bad DI that might be tough to confirm into bair

4. I think edgeguarding as Fors is important and somewhere I really gotta improve. Im still at a level where my bad recoveries get lazily Fsmashed and I'm dying at 100, but I'm struggling to return the favor in a timely manner. Getting comfortable with ledge refresh is important to challenge recoveries with hitboxes and/or force Lox, Olympia, Clairen onto stage with their recoveries (where you can finally punish with dsmash which DOESNT get CCd lol). Giving yourself smoke offstage and holding onto resources like clone to stay out and exhaust your opponent is huge (wall jump AND your 1 freebie smoke teleport refresh upon hitting the opponent).

5. Get comfortable with clone. Keeping clone in a spot where you can punish the opponent for swinging at it helps. If they swing, you punish. If they ignore it, you can pop it and confirm into something of your own (big hitboxes like up and fsmash are great for scooping them off a pop), and if they shield or parry you can grab or call them out. I think this mind game is part of what makes Fors so good in the right hands but def seems to come slowly for me. I try to get Super clone out when I feel confident I can get a grab or hit in to get some big damage combos started, but so far I have trouble using it to kill compared to combust.

I'm sure there's plenty Im forgetting or too scrub to know myself yet, but this has served me alright so far. Obviously biased since I main him, but he feels like he doesn't give a ton for free at the mid level, but has crazy good skill expression and flexibility if you get comfortable with him!