Firstly, make sure you have at least 3 GK.

Secondly, I also recommend having a fair few STs as we all know they like to recommend ST.

Most importantly though, if you want a particular position make sure you have that position in your formation.

For example, today it's nearly the end of the week and I was yet to receive my recommendation. I really wanted a DMC as I have none (so obviously not in my formation).

Before the reset I changed formation to include three DMCs (doesn't matter if out of position).

Today I received DMC/DMR 19yo with PM SA!

I had also removed positions that I didn't want from my formation and ended up with:

GK
DL-DC-DC-DC
DMC-DMC-DMC
MC-MC-MC

I only had one MR and one ML in my whole squad but they are my two best players so I didn't want more in that position so very important not to have those positions in my formation otherwise assistant manager would realise I have no subs in those positions and possibly recommend that for me.