In oil painting, solvents speed drying time and oils slow it down. Work with more oil in the upper layers and more solvents in the lower ones. Fat over thin is also important in acrylic painting. Use gels that slow drying in the upper layers. If the composition is still interesting then it is successful.
Good composition works from all angles.
Squint to evaluate value . Color can sometimes confuse and squinting helps to limit color so that light or dark value can be seen. Check to see if the corners and edges seem incomplete. If they are not well painted, it will impact on the entire painting. Make every inch of a painting just as important as the one next to it.