OK, I'll bite. Here's my thoughts:
Establish a baseline.
As an early-stage company you have no idea who your real customers are, why they will buy or how they're going to behave. You have some vague ideas - really, hypotheses - but you don't have are data to validate whether you're right or wrong. So what should you do? Run experiments to gather the required data and prove or disprove your hypotheses.
For example, if you believe that 1 in 100 visitors to your website will register for your email list, then drive 100 visitors to your site via an inexpensive Google AdWords campaign to find out if you're right. Or if you believe that if you charge $50 per month instead of $100 month you'll double your sales volume then pick up the phone and talk to 100 prospects to learn if that's true.
Structured experimentation is your friend. Learn to use it well.
Learn to love CPL, CPA & LTV.
Learning how to measure (and understanding the impact of) your CPL, CPA and LTV allow you can build a reliable model of your sales funnel. And if you can do that then you have the knowledge required to establish a repeatable process for revenue growth... which investors will love.
Be disciplined enough to stay focused on sales enablement.
When it comes to marketing, your #1 goal in a startup isn't to scale, it's to enable your sales process.
As I mentioned above, if you're early stage then you don't know who you're selling to. Therefore your marketing efforts need to be nimble enough to experiment and support your sales team (or if you're a software as a service or e-commerce company, support the online sales transaction). How do you do this? By focusing your creative, strategic and tactical expertise on anything and everything that makes it easier to close the deal.
This includes but isn't limited to:
The list goes on and on, but the point is the same. Enable your sales team to talk to the right kinds of prospects and get a strong sense of what wins you business. Once you have a feel for what works, then explore ways to scale your messaging via broader reach and frequency.
It doesn't matter if it's sexy. It only matters that it works.
It's very easy to fall into the trap that shiny and exciting marketing is effective marketing. That's total BS, especially for startups. Don't waste your money on big splashy advertising campaigns or events. Build great products and services and then learn, incrementally at first, what wins paying customers. Then you can apply those learnings to your future marketing and advertising communications. In the end, you'll be much more successful for it.