Hi Kimberlee,
Marketo Sales Insight picks your best leads and contacts based on their priority. A lead or contact's priority has two components -- urgency and relative score. The flames and stars are visual representations of these values for a given lead.
The urgency and relative score tiers are automatically calculated every NIGHT on Marketo servers. So you might want to wait for a day or two. Also check in Marketo if the leads have high score if you are expecting a bunch of stars...
This article can be of use.
https://community.marketo.com/MarketoArticle?id=kA050000000KyvX
Hope this helps
Rajesh