"Make recommendations on how to" in that sentence is perfectly fine.
Another way you could phrase it would be
Please make some recommendations on how to ...
But they mean the same thing.
The only thing I think you might want to change, depending on what you really want to say, would be later in the phrase. If you're asking about your language skills in particular, you really should specify that:
Please make recommendations on how to improve my language skills.
Or "our language skills", "her language skills", etc. In this case it would be considered normal to say whose language skills you're asking about. If you don't say whose, that will probably be heard as intentional: that you aren't asking about a specific person's language skills, but about any person's language skills. For example, when a teacher is asking, but isn't thinking about any students in particular.