I have used cheap flights keyword on joy-travels.com/air_tickets_flights/ suggest me how many time spend that keyword in top 10 position in google.
Time spent will be 4months atleast Because you will need to do link building and then later add content and On page optimization All if done well and seriously for next 3 to 4 months will help Because google takes it times to make updates so you need to have patience as well as consistent efforts
Get maximum number of back links with anchor text (cheap flights). Keep doing it. and update your site each after 2 or 3 days with new contents.
Get as many related backlinks as possible with the exact or very similar anchor text to that page. It's a good idea to create satellite sites to support your main site. Hosting and domains are so cheap.
create anchor text back links from high PR theme based sites, high PR directory also helps helps you to get top ranking
I think Putting your main keywords in the title of the page is probably the most and very very important step that affects ranking keywords...
To get on top on any of your keyword I suggest you to consider an on-page optimization as a key. The site and keyword density plays vital role in search engine. If your site page content doesn't contain a required density it becomes really difficult to get on top. And then comes link building, try to generate a niche links with high page rank.