Ordinary casual clothing is most common amongst skaters. I would generally suggest jeans and a t-shirt, followed by further layers if it's cold. Dressing in layers is best, so you can easily adjust the insulation for comfort. Skating is exercise, so you'll quickly warm up.

Here is a sample winter setup I use myself, you may wish to try this and wear more or less as appropriate to you and the weather conditions.  I tend to feel the cold more than most.

• Jeans over long johns or tracksuit.
• T-shirt (or a technical base wicking layer).
• A fleece.
• A windproof jacket.
• Gloves
• Woolly hat.  You lose up to 50% of your body heat through your head in winter, so this is an important way to keep warm.

Summer clothes:

• I tend to go with a t-shirt and shorts
• Carry a fleece and/or a windproof jacket in case it gets cold or for the evenings.

Actually, if I'm completely honest I tend to wear cycling lycra a fair amount since I cycle some distance into the park.  Perhaps not the most stylish of clothing to wear, but it works very well in keeping me dry and warm in most conditions.

Pads

Most important of all is protective gear!  You require knee pads and wrist guards as a minimum, elbow pads and helmets are recommended.