From an investment perspective:

High ROI: Your business has the potential to make big returns for the investor
Tax Benefits: Your investment is eligible for SEIS or EIS tax relief
A good fit for their portfolio: Your business aligns with their investment thesis and doesn’t cause an imbalance for their existing portfolio of investments. i.e if they have already invested in a pet food company, they may not want to invest in another as it’s good practice to spread your risk amongst different sectors.
Something that piques their interest:

From a business perspective:

Clarity: You can clearly explain your business
Credibility & edge: You have a strong team that gives you an edge over competitors
Passion: You care deeply about the problem you’re solving and you have an inspiring and unshakable vision
Focus: You can showcase possibilities of growth whilst staying focused on bringing one thing to market at a time
Proof: You have proven your hypothesis, and are seeing the beginnings of traction or product/market fit
Route to market: You have figured out options for a route to market and how much of the market you can potentially acquire
Business Model: You have figured out an initial business model that explains how your business will make money
A thought-out plan: You have a planned roadmap of activity, key hires, sales strategy, and you know how you will spend the investment money

The definitive guide to raising angel investment for your startup

From understanding your options, to finding angel investors directly.