Trial and error hasn't worked for me to be honest. It's just led me further away from ecigs.
I hate to be the only one who didn't get hooked so fast as everyone else here.
But its true, its not a fail-safe alternative to smoking as everyone proclaims.
Vaping won't work for all people. But, for those who sincerely want to make it work, it works for most people. Some make the switch with the first puff. Some, it may take months. You've invested enough money and time that I'm going to assume that you really would like for this to work, no matter how frustrated you have become.
Trial and error will work as long as you combine it with education. You need to find out what exactly is not working, then find a solution for it. You may be able to fix what you have. Or, the solution may be to buy something else.
It sounds like you have good batteries (eGo-C Twist). And, inhalation technique has already been explained to you in this thread. Juice is something you'll have to experiment with to get the right PG/VG ratio, nicotine strength, and flavor for you You've already had some suggestions for that. BTW, the flavor that did it for me was Caramel Macchiato from DFW Vapers.
As hard as finding the right e-liquid is, at least it's a fairly simple matter of trial and error. Juice Deliver Systems (atomizers, cartomizers, clearomizers, carto-tanks, . . . . . ) are more complicated. We each have very different preferences. The best place to get to know what your choices are is here:
Proper terminology - Is it a carto, a tank, or what? A Guide to Juice Attachments
It looks like you have a T2, which is a top-coil clearo. I happen to like the T2. Some people prefer bottom-coil clearos instead (like the ProTank or Evod). There are countless options nowadays. But, whatever you get, you do still need to learn how to use it, how to troubleshoot and fix problems.
I agree that the ideal would be to go to a B&M in person and get some help and guidance. I also think you shouldn't put all your eggs in one basket. IOW, try a variety. As long as you already have the Twist, you can buy one of this and one of that to experiment with different toppers. For times when you're frustrated, maybe a 2.0 ohm cartomizer. It's simple and reliable when you need to take a break from finicky clearos.
You might also get a few atomizers for dripping. I happen to love using just an atomizer and drip-tip and just dripping. Pure and simple. But, even if you don't like dripping, it's good to have the atomizers handy for taste testing new juices before you commit a clearo or carto to a juice that you may not like.
I was lucky that my brother did lots of research before he tried vaping. Whatever he bought I bought. I started with an eGo-T. Then a 510 with atomizers and cartridges, then 510 cartomizers. Any one of these might have been enough to keep me off cigarettes. I'll never know because I kept looking just to be absolutely sure. I was afraid that if I got dissatisfied before I had a new thing to try that would be the end of it for me.
About a month in, my brother (and I) discovered the 306. With a 306, a drip-tip, and my Caramel Macchiato e-liquid, I knew I had made it.!
I had smoked for 37+ years and had given up ever being able to quit. If I can do it, anyone can do it! But, I couldn't just throw out my cigarettes to start. It couldn't be all or nothing for me. I had to make it an adventure with my trusty cigarettes sitting right there waiting in case I needed them. Some people are the opposite though.
Experiment and find out what works for YOU.
... after I'd wasted gobs of money on other things (that I won't mention here, in case there are fans - except the JoyeTech 510T starter kit, which everyone knows is *junk* LOL)
I love 510-t atomizers! They're great little drippers!