Our advice is to start with what you know, what you`re strong at, and then do a little by yourself, meeting new people, and eventually expand into something that`s related but still draws on your core expertise. Here`s my wife`s path, with my help along the way, to her now successful "startup" business:
1 - college, finance and accounting degree, with German and French
1 - graduated, systems engineering training
2 - computer consultant
3 - stopped work, raising 2 toddlers
4 - computer consultant, part-time
5 - stopped that, raising 3 kids
6 - took accounting courses, to get CPA
7 - stopped that, raising 4 kids
8 - found brief, part-time freelancing work (Elance), bookeeping and database management
9 - got real estate license
10 - started helping mother with online real estate business, and then helping friend with online screens business
11 - started helping husband with marketing stroller invention (slingwheels.com)
12 - provided virtual technical recruiting assistance
13 - started a computer training company (whizkidsllc.com) for kids
14 - expanded computer training to adults
15 - started local online directory, got into blogging/advertising (dullessouthonline.com)
16 - started mom-force community/ebook to both help others, and get some help (mom-force.com)
17 - responded to craigslist ad for computer help/SEO, provided SEO help to a small company
18 - started providing SEO help to more companies, in addition to more local business website help, and technical consulting
19 - slowed down the computer training company
20 - started Internet Marketing businesses (kmeinternetmarketing.com) - focusing first locally
21 - now running a successful Internet Marketing business, offering service, consulting, training, all leveraging good systems engineering methodology.
This was over about 10 years, and 4 kids - but it all came back to the initial training and "expertise", and where she ended up was very much a "filtering" process, with many starts and stops, but very constant and motivated activity all along. Note how she got to a brand new industry (SEO) from her related position of strength (systems engineering).
So leverage what you`ve got.