Whilst there’s really no general rule on the type of clothes you should be wearing whilst lifting weights, it is still better (and more comfortable for you) if you stick to wearing clothing that is form-fitting, so you can move with ease and without too much restriction. Another benefit to wearing clothes that are more form-fitting is that there is less likelihood of the clothes getting caught in the equipment, as stressed by bodybuilding outfitters like Never Give In (check out their range of clothing at http://www.nevergivein.co.uk). Also, by wearing clothes that fit well and mould themselves to your shape and form, you can more easily watch what you are doing in the mirror and have an easier time in assessing your technique.