Speaking from personal experience here (bootstrapped, not startup, but should apply similarly):

Good:

- honesty about the reason why they wanted to start the company: "I wanted to be a owner and not an employee anymore" and "wanted to do something that will make me rich in the future even if I struggle now" are as valid as "I wanted to help the disabled better navigate on public transport" if they are indeed honest replies. This shapes the management culture in your new company and you will definelty notice when things slip away. Put them in writing, sign them, and keep track to make sure your activity steers towards these goals.

- do they work, or do they order others to do their work? It's simple, a co-founder should put in the effort alongside everybody else, and lead by example. When something needs doing their first instinct should be to work together with others and not just delegate. This should change when the comapny grows beyond a certain size as they need to focus more on upper managemnt work, but the desire to roll up their sleeves and knead the bread themselves tells you how they will treat you, as a worker or as a partner.

- do they care about the result or the process? They should care way more about the result that the process overall, but should focus on both. In particular you should set a minimum standard of quality you expect from the company overall and not micromanage beyond that. This shows how much trust you have in eachother.

- You always have to arrive at a consensus, with compromises on both sides of course. But at the end of a discussion: you solved the issue, the decision pleases all parties, and it matches the vision. It's you together against the problem, not you and the problem against the other. This sounds like marriage advice because it is.

Bad:

- not having a plan. "I'll figure out what to do after I create the company" or "I'll do consulting/outsourcing until I come up with an idea" might bring in cashflow, but then you're just another ordinary company, there's plenty of these around, no need for yet another.

- not sticking to a plan. You should adapt to market forces of course, but if you jump from project to project, from idea to idea, from industry to industry on nothing else than your short attention span you're wasting everybody's time.

- do not project your fears onto others. This had many simptoms: micromanagement; making everybody follow a complex process you developed because that's what you fell comfortable with even though it slows them down; forcing someone to develop somethig in a technology you know even though they don't know it, while they being an expert in another which would fit just as well, just because you fear you can't take over when they're away sick, on leave, or if they resign. You are no longer the "sole developer doing anything and everything your way" and won't be able to anymore. Once you bring in a few people you will no longer be able to go back to that state, so make use of people's strenghts instead of forcing them to train in your own.

Ugly:

- nepotism. It's ok to hire people you know because you trust them and they do good work. It's not ok to hire people just so they get paid, because they're "your people".

- rest and vest, the kind where you lie about working. This is extremely easy to spot and is what damages trust the most. It's basically nepotism for yourself.

- starting conflicts based on emotions and not facts. Needless to say, if you acuse somebody of something or if you think you deserve more of something, come with numbers, not a raised voice.