Take a close look at just what it is you will be using it for. How far will you be flying? Where are your typical destinations? How many people will you likely carry? Where will you keep it? These are imperative to have answered well before even looking at your first jet. Another consideration is corporate leasing. This alternative is for corporations that want to avoid the hassles that can be involved in ownership.
Look at used jets. These will all come with maintenance records, logs of service, hours flown and any FAA-mandated fixes that were done. A heavy inspection will be needed prior to any purchase, new or used. Again, there are different planes for different uses. Gulfstreams tend to be used for long-range flying, with some of the newer ones capable of United State to Asia flights. Lear jets are fast and get up higher in altitude, but have a shorter range. Either if these comes with interior configurations that can be tailored to your needs. There are smaller jets that can be considered as well, but you give up range and passenger amenities.
Begin your purchase. Get all the above-mentioned records, begin the registering process, start your corporate flight department and keep meticulous records of everything you do. Check the avionics package in the plane to make sure it is capable of flying in inclement weather. For your crews, find a chief pilot who can do the hiring. Have a corporate operations manual written to outline your procedures. Find hanger space and set up a contract maintenance for your corporate jet. You will need a flight department that is capable of dispatching your jet. This will entail getting clearances, filing flight plans, getting weather, fuel needs and crewing issues (see Resources below).