Honestly, I'd stay I away from stretching sore/stiff muscles. One of the best things to do is to keep moving. Do very light cardio., mobility work, and some foam rolling (if you can handle it). This will increase blood flow to the area and speed along your recovery process. The first two weeks are the worst in terms of soreness. Keep it up and keep moving through it. It will get better

I love my foam roller after a good hard workout. It really helps to flush wast products from the tissues and can cut down on soreness the next day.

As long as you are warmed up and not stretching cold muscles. Well, and as long as you aren't stretching a pulled/injured muscle. Its up to you to determine the difference between soreness/discomfort from working out and pain from an injury.

Start adding some stretching in at the end of your workout and gradually increase the intensity of your stretching as you become more comfortable with exercise.

I don't know what the experts will say, but I have successfully reduced muscle soreness with a heating pad.