If you do SEO yourself or contact a SEO professional, first thing you need is to know through what search keywords your product or services can be sold through Search Engines. If you hire a person, then work closely with the person to give an idea on what all service you offer and how much you can offer.
As a business owner you are the person who knows everything that can be offered and you will be knowing limitation if any. Suppose if you can only sell your service to limited customers or can sell only minimum number of products a day then you can go for weak search keywords were you have a user hit between hundreds. Weak keywords with right optimization can brig results easily.
Before starting SEO, think about you or your business strength and start your campaign. If you can offer service or products larger in size then it is well and good to start with a combination of weak and strong keywords that has few hundred and thousand users hits.