Experience, results, recommendations from prior clients but most important the ability to communicate and negotiate. The process is very straight forward in most cases that said I would also consider going to the 14th Floor of the Daley Center for the entry and detainer call to observe the process.
The most important skill for an eviction attorney is attention to detail. It can be a straightforward process, but only if all notices are technically correct and proper procedure is followed. Otherwise, it can be a long and drawn out process for you as a landlord. Even if everything goes well, expect the process to take three months or longer to get that tenant out.