SEO result within 1 month & ongoing

I m starting a new website and I need an SEO join in to plan the website from SEO purpose and then once the website is launched get us fast ranking. The domain is already 4 years of age with a website already on it and indexed by google. We are just changing our line of business and needs ranking for the right keywords.

I need fast rankings for long tail keywords within a month while you continue to get us ranking on high competition keywords within 3 months.

I will like you to be responsible from planning to successful executiion of SEO and results.

This is 3 month assignment. Might be extended depending on the result you achieve.