Being new to quilting, I've read a lot of posts about whether or not to prewash. So far, I haven't prewashed, but would like to start. My question is, if you do prewash, do you use detergent (and fabric softener) or is the primarily to get the fabric wet and then dry?

Personally, if I prewash I do not use fabric softener but I do use laundry soap. I wash the fabric the same way the quilt will be washed.
I don't use fabric softener, because I never know whether or not I will use it for fusible applique. Some fusibles stick better without the fabric softener in the fabric. :D:D:D

Me, too, amma! I wash but no fabric softener.

I began washing my fabrics when I found out that they spray the fabric with bug killers when it is imported into the country. Much of what we use is imported without knowing it. I for one do not like the idea of handling that chemical daily.
I do wash mine. Especially batiks because of the dyes that like to run from the process they use.
But, if you want to just test a small amount to see what it will do when washed, that could save you hours of ironing if you are in a hurry and the quilt isn't an heirloom in the making.

Here is my take on fabric softener. No need. Especially if you are going to be starching it. think about fabric softener is to make fabric soft and stuff. Starch is supposed to make it stiff and not move. Washing is up to you, but I would defiantly not use fabric softener.

I have become more of a washer, with soap only. I used to LOVE the feel of my new fabrics, never wash before I cut. I have realized that at the factories, when a bolt is wound on the center cardboard, one side of the fold is slightly stretched. When you cut without washing, one half of your (i.e. 3" strip) will be straight, gradually going to off of the grain by the time you get to the other side, when opened up, to the 42" across the grain. Hope this makes sense. You can do a sample washing by taking 1 yard, carefully cut; wash it; dry it; then hold it up (before or after ironing) and line up the selvages. The fold hanging at the bottom (center) will look a little twisted; I usually have to realign the selvages to make the twist go away and now my cut edges are offset from 1" to 2". I worked in a fabric store and I could see the twist on yard dyed plaids. You would cut the yardage on the plaid woven lines (which would be a true cross grain) and the edges would be off as wound on the bold. This isn't true for printed on plaid designs. Now this all being said, I still don't wash everything! I know some better, but I don't always do better!

I don't use fabric softener anyway but if I did I guess I would pre wash fabric separately from clothes and towels to avoid using it on the fabric. As it is now, if I pre wash I throw it in with whatever's getting washed at the moment (as long as colors are similar).

When I prewash, I make sure to wash everything - when I don't I don't prewash anything. A lot depends on color intensity and end use. Lately, I have done more and more prewashing because I got involved with swaps where prewash is a must.

I don't use soap unless it is a full load. (Most of my pieces are run through the sink). The reason for NOT using softener is that some applique iron-ons react badly to softeners.

I wash all fabrics before using (I tend not to buy jelly rolls or other pre-cuts except fat quarters), but never use fabric softener on them.

I always use a mild soap like wool wash and if the fabric bleeds badly add salt and vinegar in the second wash and let it sit for 1/2 hour or until it stopped bleeding.