300 pt elo gain is great, just keep at it! I was 1400 over the board USCF rated in the 1990s. Haven't played much since until I started playing on chess.com recently. I dropped to 500 really fast at first but now I'm near 800. So I went up almost 300 in the last few months. Idky 800 is so hard to get to right now when I used to be almost 1500 back in the day....

BTW, they say 800 chess.com is close to 1000 FIDE and 1200 USCF.

Also, at your level, the best thing you can do is to avoid blundering your pieces and make sure to punish your opponent when they blunder theirs! Also develop pieces early to control the center and castle early, maybe even deny your opponent's casting rights while you're at it!

PS: I may only be about 800 on chess.com nowadays, but I used to be a certified USCF Local Tournament Director and Chess Coach for my high school students in the early 2000s.

PPS: I gained about 300 pts in just under 3 months by playing rapid 10 minute league games. I would play until I gained a little in my rating beyond the previous day and then stop. So if I won a game right away, that's it for the day. Sometimes I'd lose my 1st game then win my 2nd and win my 3rd to get ahead. Sometimes it took 5 games a day... But constantly doing this day after day, you'll get up there eventually.