Start with a clan arm, your eyeshadow, a primer, makeup remover and a good lamp or sunlight, a camera or phone(i use my HTC aria) sunlight works a lot better...
start by priming your arm, you dont have to do this, but i like to sincew i wear primer daily.
run your finger(s) across the eyeshadow, but dont push to hard. i like to use my middle 3 fingers, then run your fingers against your arm to create the swatch, remove the eyeshadow with MU remover between swatches.
lighting in pictures is important. i prefer to go outside in natural sunlight. taking pictures at angles, not just straight on can help catch every little shimmer in a shadow and a swatch. take as many pictures as you like, you can always delete bad ones later.