What did Mr. Collins advise Elizabeth to do before dinner at Rosings?

From the text:

`Do not make yourself uneasy, my dear cousin, about your apparel. Lady Catherine is far from requiring that elegance of dress in us, which becomes herself and daughter. I would advise you merely to put on whatever of your clothes is superior to the rest, there is no occasion for any thing more. Lady Catherine will not think the worse of you for being simply dressed. She likes to have the distinction of rank preserved.''