If you make a habit of filming yourself from the side, you can judge a lot of your technique yourself.
Start not by looking at yourself, but at the bar. Your aim should be to get the bar in a straight vertical path. If you spot any deviations from this line, you can start looking at yourself and what is causing the problem.
To judge timing, you just create mental checkpoints. In the clean, it would be something like "when the bar reaches its highest point, I will be in a full sit with my elbows fully extended". You can judge this the same way by filming.
It's a good idea in general to film from the side, since the technique you can spot from any other position is minimal.