The Way Of The RFP
The overhead required by responding to RFPs makes this a large firm strategy. There is a tendency to commoditization, so you need a large volume of work to be profitable. This is your father's Way, but it will be around as long as there are institutions.
The Way Of Relationships
This strategy can work for any size firm. Social Media and electronic media are tools that support this strategy. You need to stay in touch with all the folks who have work that you want to do. Get to know them. Then find a way to help them so you are the go-to guy/gal. Social connections help.
The Way Of The Niche
The barrier to developing a niche used to be the high price and difficulty of establishing your expertise in the minds of your potential clients. Brochures, mailings, conventions, face to face meetings were the tools. Now the tool is writing a blog to showcase your expertise with a business type. So what once was a large firm strategy because of the cost can now be pursued by anybody.
This article about the 4 Value Propositions for ANY business might give you some ideas on how to differentiate yourself once you have chosen a business development 'Way'. However, not all value propositions apply to each of the three 'Ways'.