@Ahmed12 it depends on which area you buy in and what the demand for HMO rooms is in that area, is it from students or young professionals then target your property at that more buoyant local market place.
I would also suggest getting a guarantor on each individuals tenancy, as doing a reference is a good check but you always have added security if you have a guarantor on the tenancy.
Taking a look on Spare Room and check the ads wanted versus ads offered and how long the rooms stay available is a good tip. Check a few different areas no more than 20-30 mins from your house and compare the room rates versus property values. This will allow you to identify the areas with the greatest profit.
Good reference checks are a must and gut feeling if you are handling the viewings yourself can not be underestimated.
Over the years I have seen many investors moving into a new market and looking to "re-educate the market" on their ideas when in reality you should be checking the local market and adapting your property investment strategy to reflect local demand.