I'm specialized in Content Marketing, Copywriting, Branding, Social Media Marketing and Facebook Ads. I helped companies of different sizes with their marketing strategies.
First we need to address the terminology:
Tecnhnically "advertise" means using Facebook Ads, but you can advertise something on Fb or Ig with a post and getting organic engagement.
Effectively doing the second (organic engagement), is every day harder due to the content overload on social media and the reduction of users attention. Every year we have less seconds of attention available to conquer our ideal target.
Some of the advices you got from the others will help: you need to create content that is relevant for your audience, engage, educate, inspire.
Videos work better than anything now and of course a decent copywriting helps too.
Using the actual advertising tools, which means using a budget and trying to reach a bigger audience, can't be explained in a few tips, there aren't quick tips to apply especially if you never did.
Focus on who you want to see your ad and on what they see, so once use as advertising medium a content that is relevant, engaging and inspiring, choose the target carefully, be clear, honest and transparent and...read Facebook rules: advertised posts have a lot of strict rules to respect in terms of topics, language..
for example on your FB or IG profile you can talk about weed freely but you can't advertise anything related to it.
There are a lot of things someone can do to do market research with few resources.
1) Internet is full of data already collected ready to be used: google trends, searches, keyword and queries analysis can already give you an approximation of "what to search". Tools like Ubersuggest, Buzzsumo, but also Google Keyword Planner, and hashtag research on Twitter and Instagram help a lot.
2) when it comes with products Alibaba, Aliexpress and Amazon can help you see what the world is buying: trending products, best selling products, most rated products...
3) More specific websites like Statista, where you can start from free but then you will have to pay
Internet IS data! Everywhere
Competitors, tricky empolyees and partners are always there in business. And not all of them are mean cheaters: some just realizes and make the client realizes they can do the job better than you.
So instead of being scared from day0 about being poached, why don't you start thinking HOW you can make your services so unique that people will just want you?
I work as a freelance from many many years, I manage work for companies and agencies located all over the world. Never pouched anyone, but there was one time when the guy who hired me to outsource some work was stealing money from the client without doing the job done (he was supposed to apply my content marketing strategy in a wider seo and advertising strategy but was putting the client budget in his pocket with the excuse that costs were increasing) so when I realized I told the client and fixed his problems, working directly with me.
What was more ethical? Not tell the client tbut in this why silently agreeing to the guy bad behavior? Or what I did was the right choice? For me there is no doubt.
Now, besides those extreme cases, my experience can also say that a client ready to hire an agency will keep working for an agency if he has any minimum result. Clients ready to go away with your crowdsourced guy that offered them the same work for 50% less of the price are worth to be lost.