Start with what is comfortable for you. Even 5 minutes will bring benefits. The first benefit is the chance to simply stop your automatic routine, the unconscious patterns leading you through life without even noticing that you are alive.
How should I dress? Any way you like, and find comfortable and non-restrictive. There are several aspects of dressing to consider. The first is comfort. Some meditations use physical activity, and many people like to do some yoga or similar exercises to prepare, so you should dress in a way that will allow you to relax and freely do any exercises.
Full Article: How Long Shoud I Meditate