Managing a small team is much harder than managing one where everyone understands their roles. First-time founders seldom give the team more importance than the idea they are working on. This causes a lot of friction in the pursuit of something great leading to conflicts and low success rates.

Not delegating enough. Building a successful company requires constantly executing on several categories - product building, market research, marketing, sales, accounting, payroll, etc. Within each category, there are several tasks (e.g., product building requires coding, designing, and gathering customer feedback) I have seen first-time founders take on too much and not execute as well as they can. Depending on the startup goals, it can be overwhelming.

For the average person starting a business, a specific problem with a specific action plan will be better than some high level market analysis or product strategy. In the beginning try to use common sense to answer questions rather than through research and analysis, which will save you a lot of time and help you reach users as soon as possible.

Comp & equity, especially for co-founders. It's an extremely awkward conversation and not an area where founders have a ton of experience. More often than not this means a scheme under which cofounders set fixed percentages without regard for any subsequent work. That work ends up feeling "unpaid" and can be a huge factor in burnout (or conflict).

Getting obsessed about little details. They lack the ship first think later mentality

Time and energy management.

Figuring out the money makers & the money drainers in your P&L

Saying Yes more than No

Decide of priority.