I like to draw out my circuits and then color over the lines after I’ve soldered them or re-checked them.
I really enjoyed this overview of electronics debugging made by MIT TA D. Elliott Williams: http://web.mit.edu/6.101/www/reference/TheArtofDebuggingCircuits.pdf
Here is a summary of the main thinking as I see it:
-Circuits cannot be wrong, if there is a problem it is “either be because you do not understand what you built or you did not build what you understand.”
-You must first understand how a circuit works before you can debug it. If you are using components, understand the datasheets.
-To debug a circuit, first establish what it is doing, this narrows the list of possible errors down considerably.
-Think, what could cause this type of behaviour? Make a list of possible causes and cross them off one by one.
-Get a fresh pair of eyes on your problem.
-Systems are composed of sub-systems. Isolate sub-systems and test them each in isolation.
-Build your circuit neatly and logically, this makes it easy to check connections and reduces noise from entering long wires.
-Use the continuity mode on your multimeter to test connections.
-Make sure you are not misusing your oscilloscope (check the x1/x10, if in DC/AC coupling, that the ground clips are attached to ground, )
-Rebuild your circuit but with all different components on a different breadboard.