Similar to exterior mold, mold is more likely to emerge in warm and humid areas. That being said, rooms like bathrooms and basements are more prone to mold. To preemptively prevent mold, use paints that are mold resistant. Should you find mold on a wall in your home, you can clean it with a simple solution of one part bleach to four parts water. If the area is large, you may want to leave the cleaning to a professional.
Prep the house. Wash the walls, remove wallpaper, patch, spackle, seal stains, dry and sand before you attempt to paint. Now is also the time to apply painters tape for trimming, lay drop cloths, etc. Remove all outlet and light switch face plates, collecting screws in a zip-top bag (good opportunity to wash the face plates all at once as well).[4] You can also buy your paint at this time. Don't wait until the last minute. It can take hours to mix many gallons of all your colors. Remember that traffic triples at your home-supply and hardware stores on weekends. Buy on a weekday if possible.
After you’ve bought your materials, prepare by removing all the furniture from the room. Next you can wash the walls and fill in any holes with spackle. Make sure to lay drop cloths or old sheets on the ground to protect the floor from paint. When you’re ready to paint, start with a layer of primer to cover all the walls. Once that has dried, you can paint with color. Use small brushes to paint edges and large rollers to cover the rest. For tips on choosing the perfect colors for your home, read on!

After you have done the multiplication, subtract about 40 sq feet per window, and about 60 sq feet per door. Divide by 400 (interior paint covers 400 sq feet per gallon). The number that remains, is how many gallons you will need. If doing multiple wall colors, then you should do this process for each room (or sets of rooms) with a particular color. 
Carefully consider the gloss level. The shiny gloss paints are easy to clean, but will make any wall blemish stand out. The flat paints will help disguise wall blemishes, but can be difficult to clean. Generally, you'll want glossier paints where there's lots of steam or cooking (baths and kitchens) and in high-traffic areas. Flatter paints are preferred for large walls and ceilings.

Painting is one of the quickest and easiest ways to give your home's interior a facelift with dramatic results. Fortunately, it doesn't have to be that difficult. Home improvement stores offer samples that you can take home. With these samples, you can try a few colors in large swaths on your wall to see the how the paint interacts with the room's natural light. Compare it against design elements like pillows or furniture to see whether it will work with your overall décor.

Paper/poly drop cloths: $2 to $6 for 9x12-feet. The best of both paper and plastic, these cloths are low-cost and disposable. They absorb paint drips while providing more protection for what's underneath. They also provide some protection from slipping. Plus, you can cut paper/poly drop cloths to fit the space. But, like paper, paper/poly drop cloths can rip more easily than plastic or canvas drop cloths.

It's up to you. Outside is much harder because it requires more prep, patience, time, help, money and of course, effort. I have been painting my own houses and rental properties interiors for 20 years, and I painted the exterior of one, once. I then had it promptly done again by professionals who said it would have been cheaper if they didn't have to undo my work first. My advice is to get pros for the outside because everyone will see it.
A single gallon of paint can run anywhere from $20 to $80 per gallon. Professionals get a contractor discount of anywhere from 25 to 50 percent. For rough siding, like stucco, you’ll need to use 10% to 20% more paint. Some textures, like wood and stucco, require extra paint because they have more surface to cover in a tiny area compared to smooth siding. Use the highest quality exterior paint your budget will allow for your project. It will look the nicest and save you money by offering better coverage and durability. Better coverage means fewer coats and fewer work hours. You’ll also go a few years longer without needing to shell out more cash for a new coat. How do you know how much paint you're paying for? Here's some helpful math:
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