While painting, one must take a few precautions, such as:
Do not use cotton rags for cleaning, use soft synthetic or muslin cloth. Otherwise, threads will stick to the surface leading to a patchy, uneven finish.
Do not apply the next coat without the first one drying, otherwise you will have a wrinkly, patchy finish as well as loss of gloss.
Do not sandpaper very hard, otherwise there will be scratches, roughness and poor gloss.
Do not apply very thick coats, otherwise there will be a thick rough finish, resulting in slow drying.
Avoid mixing paints yourself. Buy readymade paints as far as possible, otherwise there will be patchy and inconsistent columns in the finish.