Looking at taking N3 this year. To that end I’m working through shinkansen master N3 grammar book. There’s a section on keigo 
something that I find difficult.
So my question to people that have taken N3, can you recall how much does keigo feature?
As far as I can recall, it doesn’t feature much at all 
I’ve thoroughly forgotten the contents of N3 last summer, but I have a feeling that there was no/very little keigo.
Maybe some set expressions like いらっしゃいませー in listening, or some usage that you can pretty much skip over in the section where you look through a flyer to find dates/times for certain events.
But to be sure you could go through some example tests online.
Maybe some dialogue in a shop/reception at most, but not much that I can remember. For me it helped by studying some of the standard verbs, such as talk, come/go, to be, to do and then pair it with some series where then use it incessently.
For the grammar section, I’m pretty sure N2/N1 have a keigo question every test. I suspect it may be the same for N3/N4 (although worth double checking against past papers). How important a single question is to your test strategy is something only you can say 