I would show great excitement when he does well, and do your best to be emotionless, matter-of-fact when he has an accident. Learning to use the toilet has a lot to do with learning to recognize your body's signals that your bladder/bowel is full and this is not always an easy task. Some kids also grow faster than their bladders and it takes time for their bladders to catch up. So chastising, shaming or telling your child you are dissappointed can be counterproductive.
One thing I did with my son is I would have him clean up to the best of his ability--take off his own wet clothes, bring them to the washing machine, give him a wet washcloth and do his best to wipe his wet skin and explain that skin wet with urine can get sore or itchy and the urine needs to be cleaned off, if he pees on the floor, give him a rag and have him do his best to clean it up, etc. Yes, you will probably have to finish the job. But the end result is teaching him about responsibility and cleaning up after yourself. My son is pretty good about cleaning up after himself, but he also rarely had any accidents because it took so much time away from playing.