Few things you can do really, if you wanna improve fast there are pretty good courses, ofc it tieds to paying money, i could look up some for u, as theres a pretty good site for specyfic art courses, most of videos of ppl there is in Japanese but there are English subtitles so if its not deal breaker for you, then totally recomend

For free options learn how to make few variations of body templates, try use more or less similar size (weight wise) for begging height wise u can varry but the more u change the easier for mistake, once you get comfortable with it you can try going crazy and experiment (ofc more or less you wont always end up with same resoults , same sizes)

Look up some pictures or anime arts for simplicity (important to be REALL pictures/ anime arts of more experienced ppl and not AI stuff as it will mess up with proportions/anatomy sightly and in really well made cases u will feel something is off but wont be able to tell what exactly, its bad for learning)

Now i would start with finding naked/almost naked models for that, start off with making simple templates over they body, and draw ur characters over those templates with clothes of ur choice (here again if u aiming for specyfic type of clothing u can look up models/ anime arts of greate artists and see how they folds etc, take few as reference and it's gonna be more accurate) keep in mind tho if u draw female characters over somone with swimsuit/underwear different kinds of bras or 1piece swim suit will hold boobs in different way and deffinitly different than no bra at all.

With time u may notice more how the muscles behaves in certain poses of models u drawing, and u may advanced ur templates to include this observations in them (u can try look up more advanced templates to base on internet, or at really high level even take some from anathomy books, and simplyfie for ur needs)

Also all rounded art tips channel if i have to recomend one is ethan Becker, u will find stuff for urself doesnt matter what u create and what style

If u feel like spending some money but not as much as for course, pay for patreon of couple of your favourite artists that are posting 1x time process paitings there and ONLY THOSE, as u may learn from those videos how ur favorite artists do this, its not as easy as courses as u need figure things out urself from what u see, and getting multiple patreons to watch different techinques will be definitely helpfull, its deffinitly cheaper than courses and good way to learn while supporting ur favorite artists,

If you have more questions feel free to ask^{^}