So you’re relatively new to casting (only a few years experience) and realizing that you've been getting by alright but when things don't go well (miscast, porosity, investment problems) you don't have a strong foundation in the fundamentals to troubleshoot what's going on. you don't really have anyone that can look over your shoulder and point out what you are doing wrong. there's so many variables that sometimes a combination of things adds up to you messing something up.
Getting my torch set correctly for different alloys
Optimal sprue technique
Most of what you cast are full gold crowns, with the occasional pfm, custom abutment, or post.
you are just wondering if anyone has some resource they can point at to read up or watch where you will hopefully notice things you are doing sub-optimally.
Here are the advice:
I would google around for info on casting with different fuel sources. Many years ago, when I was still new to this world, we were using acetylene(!!!!) to cast with. It was dirty and we were having miscasts. I started googling and found a father-son duo who had a great article about casting with different fuels and found out real quick that acetylene should not be used 
. We changed over to propane and oxygen. Natural gas should be fine also.
Spring is the other big concern. Making sure you have a big enough reservoir is key. Also keep in mind how your molten metal is flowing. I try to limit the number of directional changes the flow has to make before it gets to the margins.
I use propane and oxygen, you can cast with acetylene but it’s much dirtier. I’ve never had access to natural gas but it works fine, maybe requires a different torch?
I cast gold crowns with a direct ball reservoir sprue. You want the ball in the center of the ring, the top of the crown less than 1/4” from the top. No sharp corners, the ball needs to be bigger in cross-section than the largest part of the object you casting. I burnout full gold at 1300 F but let it cool to below 1000 before I cast it.
I cast copings for PFM’s on runner bars in oval rings, again, no sharp corners and keep them angled back relative to the direction of spin. I burnout those rings at 1400 F, I preheat the alloy and crucible in the burnout furnace with the rings.
If you are casting high palladium alloys be careful with the 02, if the torch is really hissing it’s probably set too high. Palladium has an affinity for oxygen.
