So much depends on who you want to reach and what you will have to offer. It also depends on your competitors and their online presence.
However, in general, here is what I would suggest ..... assuming a minimal initial product or service offering and a general population audience:
1. A website with a home page that establishes your company plus introduces your product(s) or service(s), plus an About page that talks about your strengths and plans for expansion, plus individual product or service pages that can go into depth on each one, plus a contact page on how to reach you. If appropriate, also an ordering and customer service page.
2. A Facebook page for promoting the company and products/services and on which your customers can interact with you and on which you can develop a relationship, especially your most ardent customers.
3. A Twitter page for interacting with potential customers, to send them to the Facebook page and website; could post recommendations, tips, or other traffic-gathering content.
4. If your product or service lends itself to community building and information sharing, I'd suggest a blog in which executives or employees, especially any with expertise, could share with customers.
5. Depending on your product or service, develop product or service demo videos and post on YouTube. Post these on your website, blog, and Facebook pages, and promote on your Twitter page. These are especially good for establishing yourself as experts in your field or as how-to instructionals for products or services. Make sure you include brand keywords in titles and descriptions.
6. Look into joining in industry forums and chat rooms to expose new customers and markets to your brand and associate your company for its expertise and product range. It's important not to be pushy in this arena but rather simply be a good citizen and help the community.
7. Google keywords describing your products or services and look for opportunities to interact in blog or news comment areas in a helpful way. Answer questions, provide expertise, suggest options, and when the opportunity arises, suggest your product or service - but under absolutely no instance do you spam these groups with product or service notices.
If you have a specialized audience - a special customer base focused on your product or service, a more relationship-based approach would be even more important. Group of people who love a hobby, for instance. Teens interested in music or video games. Seniors and travel or saving services. Do it yourselfers and project kits. Developing a relationship with a community would be perfect for blogs, Facebook, Twitter, and forums.
To simplify into bite size chunks ....
1. Nail down your product/service DIFFERENTIATION — to clearly separate you from all of your competitors.
2. Build an attractive, compelling, professional-looking website that clearly and powerfully communicates that differentiation -- and also makes you look bigger than life.
3. Find out the best ways to get that differentiating message in front of your target market as regularly and as frequently as possible -- at least multiple times every month. This may be via online or print ads, emails, press releases, etc. — preferably all of the above.
4. Create a really nice brochure -- ideally in both print and PDF form -- that also gives the same differentiation story in an impressive, larger-than-life way. The PDF version should be downloadable from your site.
5. NEVER refer to yourself as a start-up. From day one, always look like an established, significant, professional company in everything you do.
For help and more information check out these resource .....
* YouTube Video Series On How To Build Your Small Business Online
* Small Business Marketing Tips & Resources On Facebook