Plastic sheathing and masking tape was not available at the end of the painting project for whatever reason, I have no idea, but you have a Paint Brush that if not cared for will eventually dry up. Last solution that works well, is to take a sopping wet rag, wrapping the Paint Brush up like that burrito you missed wrapping up earlier. This will buy you some time until either you use the paint brush again, or you can properly clean it. OK, let's get started. Step one...supplies. You need a flat brush, a fan, a small detail brush and a couple of Filberts. A filbert is a rounded edge brush that lets you maneuver the paint easily without going outside the edges. Ultimately buy brushes that you like though, and make them work. Fans allow you to blend, for example. I use fans a lot and it's how I graduate color throughout my images. Everything I paint is by hand....no airbrushing or assistants. I want it to be an expression of me and nobody else. You also need an oil painting medium to mix with the oil paint to make it more fluid, and to speed or slow the drying process. Whichever you prefer. Go to the art store and don't be afraid to ask for help....they'll love helping you! A medium is merely an additive liquid which increases gloss, makes it flow easily, preserves the finish over time, keeps it from yellowing. I personally love Galkyd and Galkyd Lite. If that isn't available, buy a medium that looks like liquid amber and is kind of thick. Don't buy watery looking mediums....too hard to work with. If you decide to do your own body work discuss it with the paint shop first. They'll probably have recommendations on the type of primer you use. Some brands will be more compatible with their primers or color coats. The rule of thumb is to stay within the same brand of paint, both for prep and color. Even the cheapest paint shops typically use a brand name on their intermediate and higher paint jobs. Find out what it is and use the same brand as your primer coat. This will ensure you don't create adhesion problems for yourself down the road.
And, its never been more important to know your colors. Why? Because color is back in a big way! Just look at the vast variety of colors in the department stores. The second part of preparation is surface prep, it addresses covering the surfaces you do not want to get any paint on. A little plastic sheeting will go along way to keeping paint off of floors, window coverings, handrails, cabinets, counter tops, etc... And, if you are not confident with your ability to paint a straight line next to door casing, baseboards, cabinets or hardware protect these surfaces using masking tape. There are two basic types of masking tape white/yellow and blue. The white tape sticks to surfaces better but, can pull off finishes on cabinets or stained woodwork. Blue tape usually will not pull off finishes but, does not stick as well, this will probably be the tape to use for most applications. Always wipe down or dust the surface you will be masking to assure the best tape adhesion possible. If you use blue tape you may need to re-rub down the tape before painting next to it, only mask off areas with blue tape that you will be painting for a given day. With either tapes, do not assume the are a force field that paint will not penetrate, use them as a reference and dry brush the paint next to the edge of the tape and avoid soaking the edge of the tape with a lot of paint, this will cause the paint to "bleed" through giving you an undesired look. If you will need to apply multiple coats of paint, on the first coat, paint as close to the tape as you can, not really getting paint on the tape. With the second coat or a one coat application, you can use the tape more of like a paint barrier and get a little more paint on the tape if you immediately remove each section of tape after painting the section, this will keep the paint from sitting on the tape and "bleeding" behind it. Also, if you get a lot of paint on the tape it is not good to let the paint dry on the tape because some paints (especially the glossier paints) will peel if allowed to dried, with the tape when it is pulled off. White tape should not be left on for longer than a couple of days and I suggest not leaving it on more than a day in areas that receive long periods of direct sunlight. Blue tape can be left on for days, if it will stay on, there again it does not stick as well and may need rubbed down again immediately before painting up next to it. Remember, you will need to clean the airless in that same fashion before you return the airless back to the rental company. Some manufacturers recommend their vinyl paints for interior as well as exterior use; others say no, not so good. There are vinyls made specifically for interiors.