I have done four of the Zuzzy 4 x 4 mats as follows:
Get yourself some cheap plastic throw cloths at Lowes, Home Depot or Sherwin Williams you would find in the paint department. Use these to lay the mat down on in your garage so you don't paint the floor or table you lay it out on. Also get some cheap paint brushes you would use for house painting. Don't purchase expensive ones as you will tear them up from all the washing and dry brushing. Can find some really cheap from Hobby Lobby or Michael's.
For paint, I went to Sherwin Williams and picked up the sample size latex paint containers of the main colors I wanted to use. I also already had some flat white and flat black at home I could mix to change the base colors if need be for highlights and darker washes. You can also ask Lowes or Home Depot for discards which they will sell very cheap. Just make sure you are getting latex water based paint with NO gloss.
First off I took the mat out and laid it on the throw clothes. I then took a moist towel and rubbed it down to get all the extra dust off of it from manufacturing. Do both sides when you do this and let it dry afterwards.
Next up I took my base color and made a 40% paint 60% water mixture in a cup for approximately the amount of wash I needed for the first run. I then washed the entire mat the base color I wanted. Make sure it is lighter than you want as all the dry brushing and darker washes will accent it in the end and brighten it up. The key is to be patient and do a wash at a time letting it dry completely over night. When you brush it, do it in circular patterns so you don't create long obvious brush strokes. Same goes for dry brushing. Make criss-cross patterns.
After a few washes of various areas and colors you will get the effect of texture coming through as well, especially with your dark washes over your lighter base color.
After the washes were completely dry, use your smaller brushes to dry brush very light layers over the various sections to make them pop out. Again the key here is patience and doing VERY thin dry brushing as you don't want build up at all due to chipping.
After all of that is dry I went back with a little brush and hit the stones, wood, rocks, etc. with regular but light painting using my miniature paints. Then washed those as well.
Overall the key is very thin layers and taking your time. During the process, you will think things aren't turning out right but as you wait for it to dry and build up the washes and layers all will come together and look awesome.
The majority of the time taken was on the washes drying and the detail at the end. The mat itself is pretty easy to paint and dry brush using large random strokes.
PS: Don't let your cat run across it right after a dark wash and have him run up your upstairs carpet......