Small businesses and non-profits very often have to do their marketing in-house by people who don't have a lot of experience in marketing. And while creative, effective marketing is a beast unto itself, here's a quick list of straight-forward things to (NOT) do.
(DON'T) Spam website contact forms with offers of service.
Forserious. If you have the time to spam company or organization contact forms with offers of service, you look really desperate. And if you're desperate, you're obviously not very good, or you wouldn't need (or have time) to seek out those contact forms to spam in the first place. Don't have someone else do it for you, either--that time is better spent on more effective marketing methods.
(DON'T) Add someone to your email list without their consent.
So you know how you get annoyed when stuff shows up in your email you have no interest in? And how it colors your opinion of the company or organization that sent it? You don't want to be that company/organization. And even for people who do consent, US law mandates that you include a clear opt-out option.
(DON'T) Ignore social media.
I hate it, too, but for better or worse, the fact is that 90% of the US population is on social media. You need to be where your customers are.
(DON'T) Ignore Google and Search Engine Optimization.
When YOU'RE looking for a product or service provider and you're not sure where to start, what do YOU do? Chances are high that you google it, right? Yep. So does the vast majority of the rest of the world's population. Get your business on Google, and then make your SEO work for you.
(DON'T) Exaggerate your popularity/capabilities/etc.
Just because you have Facebook likes in Germany, Canada, and Japan doesn't make you 'World Famous,' and boasting such a claim makes you look... well, to put it nicely... bad. Similarly, just because you own a camera and can press the shutter button doesn't make you an experienced photographer.
(DON'T) Forget to proofread.
Nothing makes you look amateur faster than misspelling, bad grammar, and misused words or punctuation. If you're unsure, look it up or use a tool like Grammarly.