I'm heading to BMQ/BMQ-L in 10 days myself, but I was able to work a couple nights at my armory beforehand.
My fellow Private who works there as an RMS Clerk and has been in the Reserves for a couple years now, came over to my house the day before I showed up to work to help me with my uniform so I wouldn't end up looking like and I quote "a bag of ****".
With your uniform shirt and trousers, go over the whole thing and cut or burn off all loose threads you see hanging. Especially on the trousers, they're everywhere. It may take you a while but it helps you look good.
Ultimately regarding sleeves, it is up to the instructor/CO whether they want you to wear them rolled up or down. As it is summer, you can usually get away with rolling them up. They are to be neatly rolled four-fingers measurement above your elbow. If worn down, button the cuffs.
Always make sure all pockets are buttoned. It is recommended to carry a pocket-sized notebook and pen in your breast pocket in case you need to write anything down on the spot.
On your uniform shirt, there is a rope tie after the last button on the bottom. Tie it in a bow, then to help hide the strings, loop the "ears" of the bow around the last button, then button it.
Your beret probably looks strange right now - a tip I was given to soak the beret in hot water for a while. Then take it out, and put it on your helmet and let it dry a while. While it is still damp, put it on your head and, while holding it on the left side, pull it down over your right ear. Tugging on it like this will help you achieve the permanent beret shape. You may have to repeat this procedure a couple times. For me, one process left it looking more like a beret.
Once it looks decent, don't forget to put the tri-service pin on the front of your beret, above your left eye. There is a spot designated for it. You'll have to cut a spot to slip the pin in the beret. Make sure it is on securely. When wearing your beret, it is supposed to be two-fingers width above your eyebrow.
You no longer have to see your reflection in your boots anymore, but you still have to shine them. You will need to put some of the issued polish you were given on them. Spend at least half an hour on them, you'll need to work the polish into the boot with a toothbrush or something of the like, and then polish in circular rotations with a rag.
Advice as well, wear your boots around the house (both pairs) to break them in.
Also, don't fret too much about looking amazing. You won't be perfect, but you'll look half-ways decent and your instructors once you reach basic training will help you out with the perfection part. Hope this helps.