There's a famous line from the movie Glengarry Glenn Ross when Alec Baldwin's character states the ABC's of sales are to "Always be Closing". This has always stuck with me and I've modified it slightly to apply to digital marketing - The ABC's of digital marketing are to "Always Be Converting".
In order to always be converting you need three things - Google Analytics Events/Goals, Audience Remarketing, and Email Automation.
Google Analytics Events & Goals
Any website analytics tracking that allows for setting up events and goals should suffice, but I'm most familiar with Google Analytics. In a nutshell, the combination of events and goals allow you to track activities and outcomes from visitors actions on your website. Together, they allow for tracking conversions (ex, submissions, sales, subscriptions, pages viewed, etc.). Using events and goals takes your analytics beyond just tracking the basics.
Events are things you want to track that involve an interaction on your website - For example, clicks on a button, add a product to cart, form submission, download file, etc. In many cases, but not all, you need an event to create a goal.
Goals are outcomes you deem as a conversion or key performance metric. If you are interested in tracking contact form submissions as conversions, you would set up an event to track these actions and then assign them as a goal. Alternatively, you could create goals simply based on the time somebody spends viewing your website or the number of pages they visit.
Once your goals are set up you can import them into Google Ads so you know whether online advertising is resulting in conversions. In Google Analytics you will also be able to see what other sources of traffic (organic, social, referral, direct, etc.) are resulting in goal achievements. This information will be found within "Acquisition" in Google Analytics.
Audience Remarketing
If you know what events and goals people are accomplishing on your website then you can put them into audiences for targeting with subsequent ads and communications. You can also create audiences based on certain pages being viewed or other conditions without the need for events/goals. This process is commonly referred to as remarketing or retargeting.
My preferred way of doing things is to enable audience remarketing in Google Analytics and link them to Google Ads campaigns so I can target people with highly relevant ads based on stuff they're interested in. I'm sure you've been the target of remarketing ads - They can be creepy and annoying, but if done respectfully can be effective.
Aside from Google Ads, all the popular online advertising platforms (Facebook, LinkedIn, Amazon) offer remarketing capabilities. Each platform will need to be set up separately, but there are tools that allow you to consolidate the platforms for managing everything in one place albeit for a price (ex. AdRoll, AdEspresso).
Email Automation
It might not be sexy, but email is still the most effective channel for driving conversions. If you don't have an email marketing program in place then you're missing out on the cheapest and most profitable marketing medium. But, beyond just sending a newsletter or promotion you need to automate your email process.
Most email marketing platforms have automation built in for setting up a series of emails that automatically deliver based on a set of rules (ex. time passed, pages-viewed, event accomplished, etc). The simplest thing to do is setting up a series of emails to deliver over a period of a few months when a person first subscribes. Having some automation will also help you be in compliance with anti-spam legislation.
Moving Beyond Basics
Once you get a handle on the basics, you can get more advanced with conversion tracking by exploring marketing automation software that links all the above things together (ex Hubspot, InfusionSoft, Marketo, Pardot). However, I recommend starting by understanding the fundamentals before proceeding with an expensive software solution. Incorporating events/goals, remarketing, and email automation will position you well before needing more complicated solutions.
