Adding to the (in my opinion) accurate messages above, the best thing that you can do on your own (and VFR) to help your upcoming instrument training is to learn the numbers of your aircraft.
What that means is that if you are told:
descend and maintain 5000 feet at 120 KTS, you don't even have to think (or fiddle) with power or trim settings.
You just set this power level, that RPM, adjust the trim to fit the bill and forget about it for a couple of minutes.
If you know your settings, when you come back to check your airplane will be holding 5K at 120 KTS with minimal control inputs and you just will need to do minor tweaks to nail it.
Learn power/prop/mixture and trim settings for particular altitudes and speed, including gear down speed, downwind, base and final.
You'll be glad you did.
YMMV...