How can I augment my image data?

Question

What are the correct and common ways to normalize image for CNN? I used to work with text and it was pretty straightforward. Removing stop words, clean text from noise, tokenization, stemming etc. There is no problem with length we can easly add padding. I am not sure how to treat images. Grey scale is much better, less data as input. Should I rotate each image for random angle? How to pick right size of image in my traing dataset? What about adding additional filters?

(my goal is to classify 2 classes with tensorflow)