look at the modder's profile and see how active they are, how they write their mods and how they mod others. Think about how you'd like to get feedback and if they'd be a good match.
Personally I dont usually go that far though and just post in queues where I'm not breaking any rules, dont plan on ranking any maps anytime soon so if I get a modder who just wants to nitpick its simple enough to just change and resolve, and try and think for myself why I made that mistake (if it was actually a mistake, obviously modders arent perfect either). dont think too hard if you cant figure out what was wrong and they wont elaborate, just forget about it and move on honestly you'll figure it out eventually if was actually an issue, better to have no idea than to think you're right and be wrong. take any and all modding advice with a grain of salt
for a new mapper try and find modders who will actually leave you advice instead of just pointing out single mistakes in a sea of them as if you know why that's wrong. they do exist. there's modding a basically rankable map, and theres modding a new mapper, different things. don't just jump on every queue that says its for new mappers either, they are often new modders who think it'll be easier, make sure they have an idea of what they are doing.
also, dont worry about shoving your work onto them, they opened their queue to get mod requests. as long as you dont break any rules they wont care.
best thing is to make mapping friends who can help you though. modding is built to get ready to push ranked more than its made for improving mappers.