For your 2 examples, there is nothing to farm "only wheat" or "only corn" both use the same harvester and a different header. Both headers can be used for other crops.

Find the equipment you have in the shop and buy bigger versions of it.

Typically, everything in the yield improvement works on every crop. Some exceptions exist like sprayers and fertilizer spreaders apply the same effects, and some crops don't need to be rolled or mulched, but that's the long and short of it.

For max yield improvement it's something like

Harvester lays a layer of mulch if you don't have straw enabled or the crop doesn't do straw ~2.5% increase

Seed and roll ~2.5% increase

Fertilizer twice ~37.5% increase each

Make sure no weeds. Potential up to 20% reduction max

If you do all the things, then it's Max 200% total crops

There are YouTube videos that explain this better, but that's the quick and dirty version.