Ask for a technical and search audit for your site to learn what they think needs to be done, why, and what the expected outcome should be. You'll probably have to pay for this. You will probably have to give them read-only access to your site on Search Console. (At this stage, don't grant them write access.) Your prospective SEO should be able to give you realistic estimates of improvement, and an estimate of the work involved. If they guarantee you that their changes will give you first place in search results, find someone else.
Before you do anything, and this is key, you need to know what makes your company unique. You need to have a clear concept of the mission of your company. You need to determine exactly what you have to offer because that’s what’s going to make you rank. It’s that simple. SEO is just like regular business. If you’re doing everything on the same or inferior level as your competition, you’re not going to stand out. If you’re not the best result, why should people want to find you? Why should Google rank you? This seems simple, but this factor is often forgotten.
Advertising with Google won't have any effect on your site's presence in our search results. Google never accepts money to include or rank sites in our search results, and it costs nothing to appear in our organic search results. Free resources such as Search Console, the official Webmaster Central blog, and our discussion forum can provide you with a great deal of information about how to optimize your site for organic search.