I'm piecing a top and have never done sashing. My question is- what is the best way to add sashing- should the long piece of sashing between the rows run the length of the quilt, or the width?

I've seen it done both ways - I think it's quilters choice!

I prefer to do the width, but it's really up to you.

it depends. I normally make the long piece be horizontal (so that I'm joining rows together). You can certainly do it the other way and have the long piece be vertical (so you're joining columns). Sometimes it will depend on how much fabric you have and if you feel like piecing any of the sashing.

agree!

i do the right side and the bottom on each block as if it was part of the block, on the outside pieces i do 3-4 sides, (4 for the corners) then i don't have any long pieces to deal with

You can make the long piece go either way. Here is a tutorial on how to align sashing without cornerstones:

http://www.quiltingboard.com/t-43921-1.htm

Having done it both ways, I find it lots easier to use cornerstones! Makes aligning a snap!

I've done it both ways, too.

I generally do sashing and corner stones so I don't have to deal with long cuts.

I agree -- sashing with cornerstones makes life much easier (less unkind words) although using Eleanor Burns marking trick it is easier to keep things straight.