I'm trying to (re)learn mid and I can't get kills

For a couple months I played mid, and during that time I got my first mastery 7, Veigar. One game my friend wanted mid for once so I let him, and I get destroyed top versus a darius. I remember my friend saying I would be good at Darius, so I thought, might a well. I played him, and something just clicked. I started playing better then I ever had in my whole league "career" and I started doing amazing top lane (i'm not saying I played challenger level, but I had played amazingly in my own terms) And, something just clicked. I tried another champ, Garen, and I played him really well. I wasn't doing horrible. Now Darius had been my go-to for a long time, and somewhere along the line I tried Sion (not that I'm too good with him CS wise, lol) but I realized I couldn't keep it up. I had to learn something else. I was horrible at ADC, horrible at support, and wasn't to hot in the jungle, since I feel it takes too much skill and planning, but that left my old lane mid. I tried playing Kassadin, like I had used to play, and I did pretty damn bad. My friend recommended I tried some mages, and I picked up Viktor. Now I didn't 'click' with him like I did Darius, truth is, the only thing i'm good at is farming. I haven't found a character I just do well and learn and pick up fast. But I still like Viktor, he is fun for what he is, but I have a problem. I stay back and hardly ever engage, maybe to poke, but that's about it. I tried to play agressive (not full blown attacking the champion 24/7, but I attacked more than usual. And I went 2/8/13 or something like that. Viktor, i feel, I'm not horrible at, I could learn him, But I can't win any fights, and because of that I can't get kills. Sure, maybe a few, but that's in teamfights when I randomly get the kill. I can't 1v1 sadly. So I don't know what to do to learn mid. I have veigar, but I want to learn something else. Atleast 2 champions? Can anyone give me some advice on how to play viktor, or recommend some mid lane mages?