Use a paddle-type drywall mud mixer in a 1/2-in. drill for this method. The masher-type hand drywall mud mixer works well if you don’t have a 1/2-in. drill for the paddle mixer.
Joint compound straight from the pail is simply too thick to apply and spread evenly. So before you start taping, begin by thinning and mixing the joint compound. If you’ve just opened a bucket, remove about a quart of the compound to make room for water. Then add about two or three cups of water and start mixing.
The best consistency for joint compound depends on its purpose. It should be pudding consistency for hand taping, and a little thicker for the final coats. For smaller jobs, transfer some of the compound to another pail before mixing so you can make custom batches for taping or finishing.
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Family Handyman
Pre-fill Gaps with “Setting” Compound
Setting-type compound is perfect for pre-filling because it hardens quickly and doesn’t shrink as much as regular joint compound.
Start by breaking or cutting out broken or crushed areas of the drywall, then peel away any paper shreds left around the edges. Mix up a small batch of setting-type compound; if you mix too much, it will harden before you use it up.
Mix it thick so it sticks in the holes without sagging. When the compound sets to the hardness of soap, scrape off high spots and lumps with the edge of your taping knife. Fill gaps top to bottom with setting compound. Also fill gaps between sheets with setting compound and let it harden before you apply joint compound and tape.
Jessica Wilkins 
