What advice do you have for someone joining the Reserves to be a drill sergeant?

Looks like your going to get a Conditional Promotion you will get lateral promoted to CPL or to SGT if you meet the requirements. The way it works is that they will promote you before you attend school and if you fail the Drill Sergeant Course you will loose your rank and get transferred to another unit needs of the army, if you pass the course you will retain the rank.

Now don't rely on that because your going to this unit you will get aromatically sent to the academy that isn't the case most of the time, they will interview you, and asses your leadership skills until you met a desired level of efficiency y leadership. If they do not think you are Drill Sergeant material they will not send you to the Drill Sergeant Academy. and normally you will take an APFT every drill weekend if you fail you're booted from the unit.

Things to be prepared for the Academy:
- Learn at least the first 3 modules of instruction by memory you will have to stand in front of your class and pitch it to them.
- Be on top of your APFT game. The standard on event execution on and performance in black and white found on AR 350-1.
- Be professional on and off duty as an NCO is a GIVEN but as a Drill Sergeant Is LAW the Campaign Hat strikes fear and turns heads.
- AR 350-1 is your Bible for training.
- Be prepared to conduct PRT every day. you may be assigned a day or it will be randomly pick the morning of.
- know that you are always being evaluated
-DONT DO DUMB SHIT

I also wonder how you will take a DI slot as E4. Do you mean you are going to try and join a training unit, and that they will send you?

I am pretty sure that going to drill instructor course is still a selection process. Part of the packet includes a letter from a commander at least O5, and demonstrated leadership ability and potential.

It will take some time to gain rank, as well as establishing your potential with your new unit.

I wish you all the best

I entered reserve component as an E4 Spc after leaving active duty as well. I went in to a Reserve Drill Sergeant unit at Ft. Benning. I spent about a year training up for the USARDSS with my NCOs who were all DS. Got a lateral promotion to CPL, went to DSS, the made E5 within 60 days of successful completion.
That being said; learn the first three modules and be able to recite them verbatim. Learn PRT backwards and forward. Marching drills.
Work on your own PRT, weapon qual, and knowledge. Ask your NCO’s to quiz you and give you guidance. Volunteer to lead PRT, lead formations and the such.
If/ when you get to DSS hook up with a battle buddy if one is there from your unit or make one. Use that battle to help you study for your exams and modules; it can make a difference.