I would tell the beginner version of myself to stop assuming. Ask the client more questions, understand the business more before you start anything. You NEED to be on the same page.
Biggest mistakes I see daily (freelancer in digital marketing) are exactly what you said, no GTM, no analytics, no data. Stabbing in the dark doesn’t work, and if it does you waste a lot of money getting there.
Conversion tracking should be setup BEFORE any advertising starts, unless you are like Pepsi and want to spend millions on ‘awareness’, then it’s less important.
What you put in is what you get out with PPC, in my opinion.
You don’t necessarily need to calculate statistical significance if you work with smaller budgets. But you still shouldn’t draw conclusions too early, e.g. don’t choose a winning ad only after 500 impressions.
Google Ads: There’s plenty of data you only have access to once you set it up to start collecting. Geo-targeting, ad scheduling and audiences are all fantastic optimization levers… if you set them up.
So get into the habit of expanding your geo-targeting, ad scheduling and audience targeting when you first setup your campaigns, so you have the data when you need it to start optimizing down the road.
Also, get into the habit of setting up negative libraries right out of the gate. Adding one-off negatives to campaigns or ad groups is lazy and inefficient.
Bonus Also: When you finally get big enough, Google “Account Managers” will start coming around giving you recommendations. They’re sales people. Take their recommendations with a grain of salt, and know their goal with you is to get you to spend more.
Check the site and back-end before running campaigns. I had a client who had taken a vacation straight after starting work with us. We launched few campaigns. Month passed. We saw great performance with leads. The guy returned and said he had nothing in CRM. Turns out he hadn’t had his site integrated to CRM and all of the leads just fell into nowhere