Playing the little fish in a market full of giant, greedy sharks is never an enviable position. However if you find yourself in a situation where you have to fight for market share with companies that are better funded it may well be a blessing in disguise. Readiness of surplus cash has proved to be a disadvantage to several business organizations.
To fight the war and at least do some heavy damage even if you don’t win (You may get the other side to make offers of settlement) you’ll have to be first focused, then creative and of course determined.

Only Fools Never Change Their Mind
Flamboyant Businessman Richard Branson would say that was what his friend and advisor Freddie Laker always advised. It is a good advice. If you believed before that you needed tons of money to be able to fight for a reasonable share of the market with the other giants it’s time to change your thoughts. Things may not always be what they seem.
The big companies may have got so much money more than you do at present. They can afford to blow millions on costly TV adverts and empty promos. They can afford to hire and pay the best over-rated ego bags around but you may not have such liberty.

But you are yet to consider your own advantages. It’s time to look at them and get into the battle for market share believing you and your company stand a chance. Can I give a mix of magical strategies that will instantly make your David-like organization defeat the goliaths? Not sure.

But what we can explore together will put your small organization in a position to outsmart and maybe even pull the rug from under the big dominating companies with a few years of consistent application and performance.
The Basic Strategy will be to identify some strengths and then to explore them as quickly and as consistently as possible.

Working On the Weakness(es) of the Competitor
Richard Branson identified that one major weapon his Virgin Group used in entering markets with already imposing competitors was to seriously look for prime weaknesses of those big organizations and to get to work quickly exploiting them. In other words they launched into such markets using the competitors’ weak points as their own strong points. A most successful example where this worked for them was the case of Virgin Atlantic and British Airways in the UK.
If you look hard enough most big business organizations have fundamental weaknesses (mostly one or two) that can be exploited for the gain of the small competitor. Once you and your team locate a weakness strong enough to give you a share of the market if you enter with the right answer by all means enter. Prepare your strategy of alternatives and push your better offering to the market as aggressively as you possibly can.

http://nairabrains.com/2011/02/17/smal-business-marketing-strategiesfighting-the-sharks-in-established-markets/