My experience in dealing with cleaning company clients is that you need good reliable staff, otherwise you spend all your time cleaning and can't grow the business.
Staff not doing the job to the same standard that you would results in disgruntled clients, and you redoing work etc.
If you can't break through that issue you will struggle to make any real profit.
Watch your prices too, many new cleaning companies undercut the competition, only to find that they just can't do the job properly for a lower price.
Finally, think about the sort of cleaning you want to do - and consider some kind of specialisation - builders cleans would be one possibility. Those companies that do a bit of residential, a bit of office a bit of heavy duty eg degreasing etc and a bit of builders cleans, seem to me to spread themselves too thinly. Be prepared to say no to some sorts of business.
Hope that helps
Good luck
Graham