All good advice from above.....
In my own experience, I use a hand command as well as vocal. I always use my right hand for hand signals and when starting out (and mixing it up a bit) the treat is always in my right hand too. "Kinda" hidden, but the dog sees it and smells it.
First off, use a really good treat, not just a milk bone, but chicken, steak etc... to start off with.
Have your dog come to you, show the treat, and then hold it with your thumb and third finger, this will enable you to use (or at least my) hand signal.
Use your index finger- stuck out and say sit AS you put your hand over the dogs head. That's the sit position. Reward and praise RIGHT AWAY....
I would now implement the stay commmand, BEFORE you start the "stand" or "up" position. That way your dog will not immediatly get up before you want him or her to get up. So practice on the STAY command. Get another treat, hold it, and I hold out my whole hand for stay. Start for a few seconds and reward, then move on for longer time.
THEN, start with stand or up position. Get another treat, and I use my index finger again, but with a motion of making a backwards "C" with a vocal command as well. Treat immediatley, and praise.
I then would mix it up with just treats or just praise, because when you are out and about with your dog, you may or may not always have treats on you. They will not know.....