when laying concrete don't skimp on the cement also don't use too much and don't use too much water if it comes to the surface thats too much.
tamp the concrete to get the fat to the top use a float to smooth it a bit then leave it till its going off, this can be 30mins. to several hours depending on the mix and temp, also if its got a damp proof membrane.
Use a steel trowel to polish it as its going hard, this will seal the surface and make it dust free. don't do this outside as it's slippy when wet.