The key is preparation. If your walls have any type of shine to them from a previous finish, you should sand them with a light sand paper.
Next, you will want to use Zinser Bin, not the latex one, for the knots. Hit each knot before priming the rest of the walls. I would suggest probably two coats, but it all depends on if the knots continue to bleed through.
After doing all the knots, you will want to prime the rest of the walls. Try to get the primer tinted to the same color as your final coat.
After priming..you are ready to paint.
As many people on this board say...use a good quality paint from a reputable paint store, not a big box store. The cost for the paint it a little more, but the way it goes on will save you tons!
Good luck! You will be amazed at the difference when the project is done.