I suggest looking through the posts of wedding pics on this site and look at the exif, posing, lighting conditions, etc. It will give you a good idea of what it takes to get a good looking set of snapshots for your friend to get the memories captured of her day.
It this is low budget and she is asking friends to do the snaps for her, she'll know that she won't get the $5k photographer type photos. That's OK. Not everyone can afford that.
It's nice that you are trying to learn what you can to make the snaps as good as possible in the conditions.
If you don't already, I suggest shooting in RAW so you have more options for editing afterwards. You'll likely have some noise, wb, etc to fix.
You are starting at the deep end of the pool, so you would be well advised to practice tons before the event to learn all you can about lighting, etc.
I'm sure others will chime in. This is a friendly place.