Your rule of thumbs for investing? Specific ROI etc?

[Johnnie Smith]

I know there are several rule of thumbs to consider when looking at a potential investment such as the 50% rule, $200/door etc. 

I have a potential condo investment I am looking at but based on the rent I can get, the ROI runs in the range of 12-18%. The comps in the building are a 1BR/1 Bath w/ parking for $1750 where as the one I'm looking at is a 1BR + den / 1 Bath w/ parking so I assume I can get easily $1850, $2000 if I'm lucky (the 18% ROI).

Thanks for any input!