First of all, be very aware that his Primary recovery is incredibly gimpable if your opponent is good. His side-B however, is also pretty punishable and both should be used when caution when recovering. -make sure you've rode out your side-B (if you'll excuse the pun) as long as you can before you jump out of it, as it - like a jump - can be stolen from you at a second's notice.
Second, learn how to play around Mechakoopas. That's not to say "learn how to use them all the time", they're a good tool, but bring power more in their set-ups and surprise factor. Learn how your opponent reacts to them, and capitalize on it. This way you'll learn if they're worth using or not - also be prepared to avoid them yourself if your opponent has a reflector or picks them up. I put this second because it's a huge problem with people who start using this character - they just can't handle when this powerful tool is either countered or just straight-up used against them.
Next, I'd suggest the obvious - learning kill moves and options. While they kinda struggle with this, they still have some good ones, and some surprising ones at later %s. I'd advise trying for side-b, up-b, hammer swing combos at around 100% as they sometimes kill (You can even not speed your kart up to let this combo at later %s.). If your opponent starts jumping your side-b, you can usually jump out of it and n-air or simply spin out to catch them off guard (Though the latter is more punishable.). -and get used to that F-smash because it's your strongest kill-move - it's incredibly good at covering certain movements too, so don't skimp on it when you're trying to catch rollers. U-smash is an incredible tool too - with a multi hit hit-box and the ability to be JCd you'll be golden for catching people off-guard for easy kills. (There are way more kill moves, honestly, I'd try training out to really test it. -and try every move. At later %s even Koops' Jab can kill, so don't ignore it just because it doesn't seem powerful.)
Finally, just get used to what's safe. Pretty basic and self explanatory, I don't wanna be seeing no side-B spinout approaches or attempts at MK setups while your opponent is approaching. Your airs are relatively good, F-air, B-air and U-air can all be short hopped, and N-air is pretty fast, lingers and incredibly good on hit and can be full-hopped. D-air is really kinda mediocre, IMO, but it can pressure shields and has a nasty land-box on it, so it's not all bad. Your f-tilt can save your skin if you're too close since it comes out pretty fast and knocks foes back, and d-tilt is just pretty amazing in general, so you probably wanna get used to using it as a roll punish or to put off ground approaches.
Now my personal tips:
Get used to using up-B offensively. Trust me, it pays.
Koops are pretty good at gimping, don't skimp on the gimp, yo.
Do not forget D-smash exists. It's pretty fast, bi-directional, and much safer on shield than a lot of smashes are. -not completely safe, but safer.
It's all about the mix-ups and set-ups. Catch your opponent off guard for an advantage and seize it with powerful follow-ups.
Remember - you can pick up your mechakoopas too! Get glide-tossing! (-and the explosion won't hurt you, either!)
Side-B can be "JC"d for a slightly faster start-up. Simple, yet useful.
(Also, use side-B slightly later into your recovery, I've had times where the pull-back from the initial move has pushed me backwards over the blast-line. >_>'')
Hope atleast some of this helps!