You will need to do your homework before going out for the search. The nature of business, the clientele that you expect, if the area is known for the services or products that you are offering and also the time and distance the cost your target market will have to incur in order to reach you.
You should have in mind the space area that you will require for the set-up. According to the nature of operations, decide the per square feet area that you will need for each employee.
Part of your homework will obviously include allotting the set-up budget for the office space and then calculating the amount that you will need to set aside for the monthly payments. (or as agreed)
Deciding the time at which you will need the space, contact professionals after laying down the essentials in front of them, location, cost, space, etc.
You can encounter situations where the combination of space, location and cost match but the availability is not what is marked as red on your calendar. Back-up plans and multiple real estate agencies will help putting such a scenario to rest.
Short list the options that finally get filtered, run a SWOT (strengths, weaknesses, opportunities and threats) analysis and then pick out the best fit with the help of the experts.