Choosing the right keywords and keyword phrases is the first and the most important step on a way to a successful website and use them in title tag and meta description. Keyword relevant title tag is important to improve search engine ranking. The keyword factor is the one that will decide whether your website promotion campaign will be a success or a miserable fail. Keywords should be simple without stuffing. Check your Keywords with Keyword Density, Proximity, Frequency and Prominence.
Use a tool like spyfu.com or keywordspy.com to see what keywords your competitors are targetting for pay-per-click. If they've been running the same ads on the same keywords for months they're probably profitable for them!