You need several large tablets of paper set up on easels and some markers.
You start with a list of things to be drawn. I find about 10-12 items gives you about a 20-25 minutes game, depending on the difficulty of the items.
Divide the group into teams, one team to an easel. Have one volunteer for the first person to draw come up. Show them all the first item on the list and let them go back to their teams and begin drawing. When someone guesses the object drawn, the person that guessed it comes up and tells you what they guessed. You show them the next item on the list and they go back to drawing.
The nice thing about this game is that when someone guesses something, the other teams keep going. It is even possible to get behind by a couple items and stage a comeback.
When one team finishes, allow the other teams to keep playing.
I like to have a couple items that are harder than the others along with easier ones.