I'm starting to play with this technique just within plain weave, but you can really insert beads into any type of warp, anywhere in your warp.
What you need:
Beading thread (I use nymo size D)
Beading Needles (I keep a 2 inch size 10 and a 2 inch size 12 on hand)
Seed beads size 11/0 (you can really do any size, but this is a good starting bead, I am using "Dyna-Mites" with this piece, they have an easy hole to pass through multiple times)
I am weaving off a plain-weave scarf and deciding to place a row of seed beads in every 6-8 inches. I start with a length of thread about 3 times the width of my warp. This is because you will be passing the beading thread through twice to put it into your warp and you definitely want extra so that you're not struggling with the needle falling off the end of your thread. My warp is about 14 inches wide, and I'm putting on around 150-160 seed beads. You won't need the exact width of beads to the warp because the warp threads will be in between your beads spacing them out as you go.
1) To start, thread your needle (do NOT double over your thread) place an "anchor bead" on the end of your thread. You will slide 1 seed bead toward the end of your thread, leaving at least a 4 inch tail. Tie an overhand knot around the bead, holding it in place. We will be pulling this bead off later, so don't double knot it.
2) Thread on enough beads to go across your warp. (Mine is about 155 beads give or take a few, it's better to have more than less, we will remove extra at the end.)
3) Find the middle of your beading thread. Slide the last bead (opposite end from the anchor bead) on to the middle of your thread. Lay into the right side of your warp. (I'm right handed and will be working right to left of my warp for this.) Depending on how tight your selvage is, you will place the bead between the very end thread and the one to it's left, OR place the bead 2 spaces in.
6) When you have gone all the way across your warp, you will probably have beads leftover on the top thread. Tug the knot out of the "anchor bead" and remove all excess seed beads.
7) Now tie together your top and bottom thread in a square knot, and with the beading needle (sometimes you need a smaller needle), pull the 2 threads back through the seed beads on your warp to secure them in (not all the way, just in 2 inches or so).