How do you actually plan a routine?

So I've been going to the gym for around 2 months now, I've trained before but inconsistently.
I'm currently going x5 a week and I'm loving it, the thing is that i don't actually have a routine, i just follow what my trainer says everyday without question.
I've been thinking of changings gyms for one that's open on saturdays so i can train x6 a week instead of 5, but that means i'm not going to keep my actual trainer anymore, so i guess i need to develop a routine
Any tips?