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nate_king1 - basically there is nothing that you cannot do yourself, and for the most part when broken down the techniques are quite simple. It is, as fourstar correctly notes, how competitive the terms are that may influence how much ready success you have.
What might influence your decision is how fast you want to see results vs how much you are willing to pay for that speed (which is not to say all SEO firms will be able to deliver quality and/or speed of results - you will have to pick and choose quite astutely).
The best suggestion I can give you, is start doing some serious reading here. Look at the top of each forum of interest for the 'Library' link which includes some quality posts. Even if you still decide to hire someone, you'll be much better equipped to spot a quality service provider, and far less likely to get 'done over'.
Continuously add new original text copy to your site... a mix of factual, historical, insightful, jovial, conceptual, forward thinking and match these with complementary links.
Everything else is just window dressing.
<added>Early in the game link development is extremely important, but the higher you climb, the more important fresh new ideas (content) becomes.</added>