I'll add my two sense:
When you start a site, only start one. Make it the best you can make it - and keep adding on to it somehow - be creative... Make it better on a weekly/daily basis - something valuable that people will enjoy/benefit from. It may actually take you quite a few months just to create the site and set it up. You're only one person, so do you really think you have time to run multiple sites that will benefit you hugely? No. Seriously... No, you don't. So please, don't try.
Whatever site you're creating, make sure you choose a domain with your main keyword within it. Google favors sites heavily in SERPs if their main keyword phrase is within the URL. Let's do a site about car audio...
Example of domain name: supercaraudio (d)(o)(t)(c)(o)(m)
Setting up meta tags for homepage...
Meta Title: Car Audio|Car Audio Speakers|Car Audio Subwoofers
(BAM... You're good for "Car Audio", "Car Audio Speakers", "Car Audio Subwoofers", "Car Subwoofers" and "Car Speakers")
Meta description: Shop car audio, car audio speakers, car audio subwoofers. Best deals on car speakers and car subwoofers!
(BAM... You're good for the same keywords)
Meta keywords: car audio, speakers, subwoofers, car speakers, car subwoofers
(BAM... You're good for the same keywords)
The page these tags are on must (M-U-S-T) have "Car Audio", "Car Audio Speakers", "Car Audio Subwoofers", "Car Subwoofers" and Car Speakers within its text - even only once each - but at least once.
Onsite page SEO for homepage... All set!
If you're serious about ranking for these keywords...
You will spend some time for the first 4-5 months. And you will spend some money doing so, but nothing to put you into debt... Invest money to make money a whole lot more money. But you need to invest in the right investments... Like the ones below.
This is how you will (And I and others I know have already done) become successful.
Search for all automated backlink submission sites/tools which allows you to submit unique content by the form of spinning (And you must fully spin well - this will take some time but is of G-R-E-A-T benefit). Use a few services for article distribution (make sure each service has it's own network of sites - simply ask them, "are you using the same network as so and so?"), a few for blog commenting (make sure each service has it's own network of sites - simply ask them, "are you using the same network as so and so?"), a few for social networking sites (make sure each service has it's own network of sites - simply ask them, "are you using the same network as so and so?"), a few for social bookmarking sites (make sure each service has it's own network of sites - simply ask them, "are you using the same network as so and so?"), and so on for other types of links (Directories, etc.)
Think of this as a full time job for you (Yes, it is work, at first). Use all of these auto-submission services as frequently as possibly, targeting the example keywords, "Car Audio", "Car Audio Speakers", "Car Audio Subwoofers", "Car Subwoofers" and "Car Speakers". Start with slow drip feeding of links for each service (5-10 per day), if you're a new site. After 2 months bump it up to 40-50 for each submission service. After 4-5 months... once Google has seen that many "people" are "talking" about your site and you've been indexed to rank somewhere in Google for those keywords... BAM... And I mean B-A-M your backlinks, and as many as possible each day from each submission service. Google only expects this (Because your site is awesome, right? Make it "look awesome" to Google - and that's how you do it!). The amount of money you'll make from your site (Because you will start ranking and also be driving a load of traffic to it simply from people finding a lot of these links), whether it be from Google Adsense clicks and/or selling products will allow you to start paying other people and link building companies to build links for these keywords for you.
But... You have to work hard at first, so you can start making enough money to sit here and type what I'm typing while others do your work for you. Get it? Unless of course your bank account is impressive already...