Correction is not harsh or abusive. For training purposes, correction is an attention-getter or distraction. It may be a quick pop and release on the collar, or a loud noise, or a spray of water. It is followed immediately after the poor behavior stops with praise and a smile. Dogs do not have long attention spans.
Obedience is hard work.
Working with your dog for 15 minutes on intense obedience can be as thoroughly exhausting as running your dog in a field for an hour or longer. Be consistent in using the commands to your dog, and be consistent in enforcing the command. Do not be so lavish in your praise that your dog loses it's little mind, but do be enthusiastic enough to keep your dog happy in its work. Always end with something fun, that your dog does well. If you like to treat your dog, give the dog the treat, after the session is over.