Photographer & clients want to be able to see your figure; so please don't wear anything flowy or baggy, so they can see your silhouette..
You basically want them to focus on your figure, not what you're dressing.
No jewelry, clean hair, No or very little make-up, they need to see your skin and your eyes.
Have a professional attitude.
Try to mach with the style of the client's product: if is a jeans wear your favourite one, if is a couture client be elegant, at least a bit...
Take your personal stuff like hat, coat, umbrella out.
When you arrive at the client: You have 2 minutes to show your portfolio and yourself.
In big job, there is sometime 200 other models before and after you. Take the maximum chances that they can remember you.
Smile and Charm.
DON'T BE LATE, NEVER!
I hope it was helpful. Contact me if you need more info.