Hi Mouna, Start by having an online place for you to meet people like a website, then a shopping cart for purchasing opps from you. Also, any online meeting places to share your message like FB, here, MerchantCircle, etc....
You can also use niche ppc and adwords which work for some but not most.
Setp 1: Add credibility to website like truste certificate, customer testimonials. Social network pages, 1800 nos, physical address etc.
Step 2.: You need to validate the market - Use google Adwords
Step 3: Optimize landing page or other pages - Use google Adwords, crazyegg etc..
Step 4: Then you can heavily focus on SEO optimization. You could start SEO earlier as it takes time to get in build it... But do not focus on SEO first before validating your market and page optimization. And for SEO keyword you need to validate the keyword with Step 2 anyway.
Step 5: Of course you can work on other press release, blogs, link building etc.
This is assuming you have website up and you are launch phase...
The best step to launch a business is start writing contents for your business,Make documents may be physical documents,start writing blogs and postings about your business.Collect the best content,Images,menus do enough research about correct content for the website and then go for a website hosting for your business.That will be the stepping stone and your online journey will start and continue with enough SEO keyword postings,web links postings and so on.
It depends in which kind of online business you want to launch, but creating a blog first its a good idea; you must decide what kind of products or services you wan to offer and test and know your market's needs. Do a little survey and share it with people you know. Use the blog as primary tool to begin beign noticed online, support it with social media. When trying to expand your audience, promote your products and services by guest posting into another blogs; that can help. There are many ways to begin an online business, but first you gotta be sure about what will you offer to your clients.
I would do a good survey to see if there is any demand for the product or service you are offering. Then, I would buy a copy of Perry Marshall's book "The Ultimate Guide to Google Adwords" and put ads on Google. If you're on a budget, join some groups on Linkedin.com where your target customers hang out and send them a personal email - first to make a connection, then after you have that, then offer your product/service. Your question is too complicated to answer in a short paragraph so I hope this helps. All the best.
The best thing is Pay Per click with seo in back ground, but I guess it all depends on funds, if low on funds try social media, but this will take time where PPC is instant.
Good Luck with your venture.
The best steps to launch a business in my opinion is start a blog. Gain an idea of maneuvering websites. Determining where your specific expertise will be. After that, determine the kind of business that you want to launch and research your field. Please let me know what other questions that you may have. Also, I recently wrote an article about this very thing! Here is the link -> http://www.yourinfodaily.com/11/post/2014/03/columpreneur-the-heart-of-your-wallet-an-entrepreneurs-guide-to-navigate.html