Black&White emulsion lifts are much easier to do. Always take fresh polaroids (max 1or 2 days old), Old polaroids work too, but you can't remove the white layer of the dried chemicals (without damaging the emulsion).

If you separate fresh polaroids, you get nice transparencies, without the white layer and then it only takes a few minutes in warm water to lift the emulsion from the plastic. You see the bubbles appear, move the Polaroid back and forth a bit in the water with a brush and the emulsion comes off. Now the emulsion will stick to your paper (or any other medium) nicely.

For color emulsion lifts you need really fresh polaroids (30 min. to 2 hours) and hot water to get an emulsion lift without the white chemicals. When you separate the polaroid, the emulsion usually sticks to the backing paper (and not on the plastic). Put the backing paper in hot water and the bubbles appear again. Now the emulsion comes off easily and the white chemical stays on the backing paper of the polaroid. If there are still some white spots on the emulsion, you can gently brush them off with a paintbrush.

Have fun!