You can find advice on the importance of preparation, priming, paint choice, etc., lots of places, including several of the links here, but I never see them mention a practice I find invaluable, so I'm putting up this tip.
Before I begin, I ALWAYS fill a mop bucket two-thirds with water and put a scrap washcloth or hand towel in it. I keep this bucket near where I'm painting or caulking. If I get paint or caulk on my hands I dunk them in the bucket and rinse. If I get paint on the wrong thing, I wring out the towel gently and scrub off the booboo. Amazing how well this erases screw-ups. Stop and erase immediately. You may be tempted to finish 'just one thing' before you stop to erase--don't. The paint dries quicker than you think. Erase immediately. A full towel is a little harder to manage, but has lots of clean wet areas to switch to. Just don't swish it into a freshly painted area.
If painting inside you'll probably want to keep the rag squeezed out--you don't want to spill water on the floor while hurrying. So, you may have to re-wet the rag occasionally to keep it ready.
Naturally, this only applies to latex (water soluble) paint and caulk.
If You've Read This Far You're Ready For Tip 2.
If I have to stop painting for a while, I don't want the brush to begin to dry out. I put it in plastic wrap. I have a box of gallon size clear plastic food storage bags for the purpose. (These are not ziplock bags they are thin plastic, like big sandwich bags, and don't have a closure seal.) I slip the brush into a bottom corner of the bag, then sort of roll it up in the bag, continuing to roll it until the bag is wrapped snugly around the handle. The objective is to wrap it tightly enough no air can get to the paint. I've left brushes like this for several hours and when taken out they're like I never stopped painting. You can also drop a paint filled roller in the bottom and roll it up in the bag. This works with both latex and oil paint, though I've had much more experience with latex.
I hate to clean brushes, so if it's going to be a day or two and I don't need the brush for something else, I wrap it and put in the fridge. If it will be weeks I've had success with putting them in the freezer. I've read that freezing brushes with latex paint will make a gooey mess -- I haven't had that problem. I've read that oil paints must be put in freezer even if it's just a day. When you're ready to paint again, just put bag and brush in a jar of hot water or under the hot faucet for a couple of minutes to warm it up before taking them out to paint again. I don't know if there is any limit to how long they'll keep like this. I've kept them in the freezer for weeks.
I'm sure Saran wrap would work for this too. You'd may have to use it for rollers if they won't fit in the bag.