Have a meeting with your main dental laboratory and get their honest feedback on your work.
Ask them what you are doing right and also what you are doing wrong and the ways you could improve.
You'll need to promise them that you won't “shoot the messenger” even if they tell you some very unpleasant truths.
A very common mistake is underpreparation for crowns. You can tell the tooth has been underprepared if you see opaque showing through or the crown is too bulbous. Are you giving your laboratory sufficient clearance?
Another mistake is unclear impressions. Are you taking good impressions?
I'm sure you get the idea.
Done well this idea can really help upgrade your quality of work.