Like Henry said, this is highly dependent on the area and the type of property.
A good rule of thumb I like to use in A areas (Lincoln Park / Wicker Park / Bucktown / Lakeview / etc.) is 0.75%. That is, the gross monthly rent should be 0.75% of the purchase price (e.g. $400K property should get you at least $3000 per month in rent). Most properties in those locations won't fit this criteria, but many will - you'll need to understand the (1) types of property configurations (2) locations and (3) the market rent / types of tenants that will work for this criteria. This rule of thumb will guarantee that you get some decent cash flow that is worth your time, even in these A class locations. The only exception is you are buying cheap $200K 1 bed condos in these areas... then 0.75% doesn't really matter because you're only getting $200-250 a unit in cash flow which is nothing to write home about.
You can actually hit 1% in these areas as well - with very little rehab and value add. But the key there is to buy below market value, which is harder to do until you have more experience and connections.