Training for a 5K

I will be doing my 3rd 5K run tomorrow since I've moved to North Carolina. I have no idea how I should be training for these events. I know for a fact that the way I "train" for them is not conventional. Before last race, I ate at a Japanese restaurant and got home at like 11 that night unbelievably full. Somehow I still ran the race with my best time. Tonight, I'm either having pizza or burgers at like 10 o'clock for dinner. That's not exactly the best meal right before a race. I know that you should have pasta two nights before you run. I had pasta last night. In terms of training with running, I only run on the treadmill to train. I only run between 3-5 miles each week, which isn't much. I am far from your typically runner. Somehow I managed to get 1st in my age group in the last two races. We will see how tomorrow goes.