Here is my method for repairing cracks. It works quite well.
As seen in the first photo, I mark all my cracks. Then, I use an old screw driver or even an old chisel and start scraping out the crack.
I chip away any loose paint and deepen the crack.
The remaining procedures are:
1-fill with plaster
3-apply thin layer of plaster, then use paper tape
4-apply more plaster on top of th tape
5-after dried, apply more plaster by feathering outat least 6 inches on either side of crack
Following these steps you wont go wrong and you wont be able to see where the crack was. As a final measure, I sprayed an orange peel texturizer (bought in spray cans) to attempt to match the rough characteristic of my 90 year old walls. If youe walls are new, you woudnt need this step.