(I will add some pics later)
Getting a good set of brushes is super important. Not only will it save you time, in the long run, it will save you money.
It seems simple but if you have a big project with a big surface area, get a larger brush. For smaller, more detailed areas, smaller brush.
I personally use a 3" brush on almost all tops and sides and drawers of my dressers. I used to use a 2" and it took forever and had way more brush strokes. So, now I have 3", 2" and 1" brushes. I really like the nylon brushes. Easy to clean and pretty darn durable.
Plan your painting to work with the brushes and area you have to paint. First, do the larger areas and then move to the more intricate areas. However, BEFORE YOU SWITCH BRUSHES, WASH THE BRUSH YOU JUST USED. Do all the big stuff first with your big brush, then rinse it out/wash it. Then do the next size brush etc.
If your paint brush is "pulling" when you are painting, that means you need to wash it. The pulling is because the paint is drying and the dryer the paint gets, the harder it is to remove. The hotter the day, the faster your paint will dry on your brush.
CARE FOR YOUR BRUSHES.
It is essential to wash your brushes thoroughly. What kind of soap you use will depend on what kind of paint you are using. I use chalk paint and latex paint. To rinse my brushes I use warm water and dawn dish soap. I also have a pink soap I got from Michaels used specifically for acrylic paints that I will occasionally use as well.
Rinse your brushes until the water runs clear, turning them so each side has been washed. I actually use a scrub brush to wash them, only scrubbing one way (away from the paint brush handle), not back and forth. Make sure you rinse all the soap out and allow it to dry before using again.
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I have recently started using sponge brushes because they show less brush marks and I can get in the corners easily. The beauty of these, you can put them in a ziplock bag in between uses and the paint will stay moist! The downside being, they suck up a lot of paint but the ziplock solution helps soften the blow since I will use the paint on the next project (or finish the current one)