The first item needed to promote your business online is naturally your website design. There are many resources that will lay out a checklist of best practices for website design, but in summary the website needs to be clean and easy to navigate.
Once the website is squared away, it needs content. Your business website needs to have a homepage, and a separate page for each product or service. This will help you rank for each service, and you should only optimise a page for 1 subject/topic.
Lastly, claim all of your local citations. This helps provide referral traffic, and in some cases can provide do-follow backlinks which can help website authority and rankings. Additionally, having numbers citations helps SERP control, meaning when someone searches your brand name all 10 results will be owned by your business. It’s important for your brand to occupy all first page results, and having Facebook, LinkedIn, Yelp, etc helps add results in addition to results featuring your own website.
Overall, SEO today revolves around proving value to users. There are many tips and tricks, but most of these will naturally happen if your focus stays on providing the most information to your users as you can. In the end, search engines provide information and will rank the most informative and valuable sites higher. If this remains your focus, improved rankings, better user experience, backlinks, and more traffic will follow.