Come and sit are the most important commands to teach younger dogs,IMO. I started teaching mine when they were 8 weeks old. I started with the come command first. I would sit on the floor on the opposite side of the room and call them in an excited way while tapping on the floor (pups are curious and need to investigate everything, including noises). When they come to me, i praise like crazy with an excited/happy voice and give LOTS of pets and rubs. Once they have a room mastered, I ventured farther away and repeated it.
It's best to work on one command first and master it, then start a new one. For sit, I would tug back gently on his collar (which they had on by the 4th week) while pushing their bottom to the floor and say 'sit'. I'd hold them there for about 5 seconds repeating the word sit then praise like mad. Also remember that pups atttention span is not that long, so training for 15 minutes a day, 2-3 times a day is plenty for them. After that, there attention flies right out the window, lol.
Just remember to give oodles of praise and do not reward when they don't do the command in question. I usualy stand still with my arms crossed in front of me. It lets them know that I'm not happy.
My pups have to 'sit' and 'stay' before getting food, water or playtime now and they do it very well.
I learned alot on how to train from this website : http://www.dogtrainingbasics.com/
Just click on Articles.
Hopefully this helps you. I'm new to training pups too but these methods have worked for me.