No, please don't misread my post, it wasn't intended to be heard in "that" tone of voice.
"This is why you can't cook liver?"
No, I used to use liver as a high value reward and freeze it in between, but this did mean every few weeks having a major liver-cooking session in the kitchen. It's pretty yuck stuff and stinks when cooking and I just couldn't do it regularly. Plus mine will work just as hard for frankfurters, so why spend 1 hr in the kitchen cooking stinky liver when I can just put some frankfurters in the trolley at the supermarket? But I've nothing against people who use liver for training and who want to cook it like this.
Really, anything you give your dog, which your dog wants, can be a reward. This even goes for things like: opening the door to let the dog outside. Taking the lead off the dog and letting it free to run around when you start a walk. Allowing your dog to go and greet another dog. All these things are rewards, in the same way as frankfurters or cheese are.
I even use my dogs' regular kibble as rewards and we train every meal time, so they earn even their meals and literally nothing is for free. I appreciate that not every would want to do that or have the time to. In which case, at least only give them the less tasty things for free, and save the tasty ones for when they have to work.
Yes, you should definitely go to a class, like others have said. I still take all mine to classes. For socialisation and for training with the distractions of other dogs around, nothing beats it. You might want to look at this link and see if there is a class near you: www.puppyschool.co.uk