HELP!!!How do you dress business causal???????

this week I am going to go to visit law firms with a program I am in. I am in high school btw, so I am new to this. The lady that called me for the trip said to wear jeans and a nice polo, but I am not sure what shoes to wear??? I dont feel that flats go right with jeans and I have a pair of new all black nikes, but that doesn't feel right either? High heels? What do you recommend? The lady also said not to dress up or wear suits. Its just a lunch with lawyers from a big law firm.