The only way to be sure is to memorize. However, you can use guidelines to make the right choice 90% of the time or more.
If there is no compartment involved, you get ON it. (bicycle, motorcycle, skateboard, etc.) (Note: partial compartments, such as those of convertible cars or open-topped boats, count as compartments; pretty much anything where the vehicle at least partially surrounds you.)
Oddly enough, if the transportation is large enough to allow you to move around freely, you also get ON it. (Bus, train, large boat, passenger plane, etc; anything with an aisle or walkway.)
Otherwise, you almost certainly get IN it. (Car, personal aircraft, canoe, etc.)
Thus, you would get IN a speedboat, but get ON a cruise ship, even though both are boats and both are enclosed, because the speedboat is small enough that although you can probably change seats without difficulty, you can't really move around freely inside it.
As a counterexample, even though a van may be large enough that it does have an aisle and you can move around freely inside it, if you call it a van, you get IN it.
Specifically for the word "report", I'd use the following prepositions... (I'm assuming that the examples are the titles of the reports, so I'm using title case.)
Report on Air Pollution [report is about air pollution]
Report of/by My Research Group [report is written by my research group]
Report to/for the Environmental Protection Agency [report is written for the EPA]
These prepositions can of course be combined:
Report on Air Pollution for the EPA by My Research Group
The question of when to use prepositions in general is too broad to cover in this site's Q&A format.
Best Answer
"Make recommendations on how to" in that sentence is perfectly fine.
Another way you could phrase it would be
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:
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.