Summarize the following:
Do this outside in the grass, if you can, to reduce cleanup. If you do it inside, or even in a garage, you may want to lay newspaper down so the dust doesn’t get everywhere. It’s also probably best to wear old clothes.  You don’t need to spend too long on this, just check for any bumps or especially rough spots. If you don’t see anything, then you don’t need to worry about sanding. Even if the pot does have bumps, you have the choice of leaving them to add texture to the look after you paint it. This is good for new pots because it will loosen any stickers for easier removal. It is also good for pots you have planted in before because it will loosen any dirt. If the pot has no stickers and you can tell for sure it is clean, it may be alright to skip the soak.  Although you’ll have to leave the pot to dry at various stages in the process, while it soaks, you can use the time to gather your other supplies and set up your paint area. If you don’t want to leave it for an hour, check it at 10 minute intervals and if it seems clean to your satisfaction, move forward with the process. While soaking the pot may loosen the dirt, used pots are likely to need a scrubbing to get them completely clean. The paint will not go on even or stick properly if there is any dirt or debris.  Your pots may need a soft brush so you don’t scratch them too much, but if there are any stubborn spots you can switch to a wire brush for extra strength. If you happen to scratch the pot any while brushing it, there’s no need to worry because the paint will cover it and even it out. Painting the pot while it is still wet will cause the paint not to stick, so set it out to dry. If it’s a sunny day, put it outside to dry the pot faster. The time it takes to dry may depend on the size of the pot. Drying may take a few hours, so plan ahead for this part so you don’t waste your time while you wait.

Summary:
Sand the pot to smooth any rough spots. Soak the pot for 1 hour. Scrub the pot with a brush. Let the pot dry completely.