What 500K 773 says is correct. Look at what your tires are rated for. But this can be personal preference as well as working conditions. On a skid steer your tires are the only suspension you have, so the higher the pressure in the tires the more bumps in the road you will feel. As far as working conditions go here is an example. I have had to drop the tire pressure down to 5 psi when digging some swimming pools in Long Beach, CA. This is because of the sugar sand. You will find this sand at 3' to 4' down. This sand is light in color and super fine. Dropping the tire pressure to 5 psi does not work perfectly but it does help a lot to add flotation. When digging pools in fine sand you will also need water. This helps bind the sand (dry sand will run through your fingers, wet sand will stay clumped together) and it will give you more traction. You will also need expanded sheet metal military ramps so when your digging the deep end you can climb up and out.It will depend on the size and ply rating of your tire. Look on the sidewall of you tire or the owners manual for the recommend pressure.
An 8-ply 10-16.5 tire should have about 45 psi.
A 10-ply 12-16.5 tire should have about 40 psi.
My 10-ply 31.5-13-16.5 floatation tires only need 30 psi.