Things You'll Need
Get the experience. Trying to start an agency without enough experience in the industry would be admitting defeat from the beginning. Entrepreneurs that have inside knowledge are going to be more successful than others are. Armed with agency experience and a degree or MBA will leave you better prepared.
Research the market. Ensure that they are enough potential clients in the area and if possible find your direct competition, so you know who to target and avoid. Make an in-depth business plan that illustrates long-term goals and growth projections as well as short-term startup planning. A business plan like this will not only be useful for impressing possible investors but also will be a guideline for you to keep on track.
Find the funding. Starting any business will require a lot of out of pocket expenses and it may take some time to turn a reasonable profit. Secure loans from banks for startup capital and look into small business grants. A partner (sometimes silent) is another possibility, as is a group of investors and your own agency earnings.
Network. Public relations possibly more than any other type of business relies on contacts. Call in any favors owed to you by others in the business about clients and openings. Although not always ethically sound, research the possibility of recruiting previous clients and companies that you have worked well with in the past.
Advertise. A lot of business opportunities are generated by networking and word of mouth, so get out there and talk yourself up. Generate free publicity by non-profit partnerships, sponsored events and community service drives. Local exposure using area broadcasts and radio will also be a cheaper option.