[alan_n]

Apart from the other tips given, in particular proper technique:

Try doing a few meals in a row with similar ingredients and chop once for like the next 2-3 days (depending on what's being chopped).

Also you can try timing yourself. See how long it takes to chop an onion, record it. Now you know the REAL prep time for a recipe based on it's ingredients.

What really saves time is having an idea what order you're going to do things and how to parallelize tasks, but for that you need to have some intuition about time so you don't accidently burn something. There's a recipe I make that takes twice as long if strictly prepped first then cooked.

Also, just going to state the obvious, but if you're cooking for more than two people, it's just always much harder.