I am trying to figure this out, but online searches don't seem to be helping. In particular what I'm looking for is something like "In exchange for helping you, please help me" or put more simply "In return for X, Y." To be more precise, used in an actual sentence: "In exchange for me helping you with your English, please help me with my Japanese."
As has been noted in the comments, 代わり【かわり】に is the construction you are looking for.
When referring to discrete objects, it usually takes the following format:
object of desire + の + 代わりに + favor performed in return
e.g. このリンゴの代わりに何をくれる？"What will you give me for this apple?"
In the case of your request, there are a couple of other ways it can be phrased to achieve a more natural feeling:
- If you're simply talking about an exchange, try using 〜てあげる代わり【かわり】に:
英語【えいご】を教えて【おしえて】あげる代わりに日本語【にほんご】を教えて【おしえて】ください。 "In exchange for teaching [you] English, please teach [me] Japanese."
- If you're already teaching them bits of English, then you can express the sentiment that you're already giving something by using the plain form of the verb + から ("therefore"):
英語【えいご】を教えて【おしえて】あげるから、代わり【かわり】に日本語【にほんご】を教えて【おしえて】ください。 "I'm [already] teaching [you] English, so please teach [me] Japanese in exchange."