I would like to make some coasters, but have no idea what kind of fabric or what to start with. Is there any special techniques I should do? Do you embroidery through multiple layers or just the top and then connect it to other layers? Thanks for your help.

Good question. I'm looking forward to hearing how everyone else makes their coasters.

I use any fabric. Linen look is great, muslin, chino etc... I put felt inbetween the two layers before I stitch it with the final die line. Have fun... Suzanne

I have done them with fleece. Stitch the design then at the step where you put the back on I also add a piece of iron on vinyl (it starts out sticky so I stick it here and iron down after all done) on the top to stop the moisture from damaging the stitching (and / or the table underneath).

I have just done some on felt. Stitched the pattern, added a second bit of felt underneath and then the outline. Then I cut round them. They are quick (OK not as durable as some I have made) and I hope they will sell on a charity sale!

The rule is - that there aren't any rules!
I made some last week using thevinyl table protector material. I embroidered the design (not too dense) and then added a second layer beneath the hoop and stitched an outline (just a simple running stitch.) I cut them out about 5mm away from the stitching.
If you use fabric you could do the same but you would need a satin stitch border and some interlining or wadding. (Muftoflex has a good outline in DBC.)
There are lots of coaster experts around here - just hang around for a bit and the advice will flow!