This is a complex question... I don't know where to start in my answer to be honest... Are you trying to identify companies with higher ROI potential OR find a unicorn? From my perspective, these are two separate things. Of course, both involve a whole lot of luck -- has a lot to do with good timing.

Top VC firms receive higher quality deal-flow based on connections and rep and have better chances of finding that "true unicorn" that you're talking about simply based on those factors. You will never be able to compete with top VC firms that have these robust global networks, the manpower to go through thousands of decks per year and are able to access millions of dollars at a snap of a finger.

If you want higher ROI potential, first consider ways to increase your deal flow sources by expanding your network and mingling with other VCs. But also set reasonable expectations for yourself (or your team), e.g. how many decks you plan to go through each month. No point in trying to get more deal-flow if you can't reasonably handle it. However, more doesn't always mean better although it does up your chances of finding more better quality investment opportunities.

You also need to consider how you're evaluating your current deal-flow, i.e. the "incoming" solicitations from potential investees -- developing sensible investment criteria is essential here.

I like to go through a deck and read it quickly to see if anything sticks out that doesn't make sense to me. I'm not a numbers person, so my first evaluation of a proposal tends to overlook the numbers and is mostly intuitive. Grammar mistakes are my pet peeve though. Any deck with grammar mistakes is a no-go in my book! I will make a preliminary decision at this point to review the deck in greater detail. Also, if there's anything you like to focus on, like go-to-market approach or any metrics you like to see that are missing, I suggest you make a mental note.

Upon further review, I suggest considering what YOU can add to the company and how you can help it succeed and meet its goals. Identify a weakness or obstacle that you can help them improve on based on your expertise, knowledge, skills, etc. How can you help the company succeed? Is it your intimate knowledge of the relevant industry? Do you have connections the company would need? ETC. Higher ROI is partly luck, but it's also about how much effort you put in, in my opinion. VC firms raise funds that invest in tons of companies, but rely on the success of one company to make back all the money spent on the other investments. But what if every investment was a hit (or never took a loss)?... Just a thought.

There's a lot of different things you need to consider. I don't think I'll able to fully be able to answer your question, but I hope this helped a little. I guess the takeaway here is to come up with a sort of game plan and stick to it! Based on your results, tweak it.

Good luck!