This is a fairly easy task, about a level 3. from 1 - 10.
Its messy and it requires two people. The drywall compound I like is 45 minute dry compound. I will water this down to about pancake mixture consistency. I will get a 3/4 inch knap roller cover and roll it on the walls. The roller is the vehicle to get it on the walls, Do not roll on too much at a time. Then after a wall is rolled, then with a 14 inch long trowel float out the wall smooth. Remember, any slight deviations will be sanded out and caught on the second pass. Allow allot of ventilation in the room.
When pass one is complete, stop for 24 hours to dry out then do your sanding smooth then a good wipe down and start the process over again. Twice should do it.
Key points, get the stuff thin enough to handle but not too thin that it runs. then the trowel the key is the longer the better. This makes less passes and for a more smooth surface and less sanding.