One thing that often happens in "hot" start-ups is premature hiring. It's a shameful waste of resources. Until your product reaches product-market fit (PMF), you should stay as small as possible regarding roles and a number of people. You should always hire "almost too late" rather than early because you expect your product to blow up.
I think hiring should always be related to your need to add more resources on the product or distribution side of things. That means a hire needs to increase your "product lovability" or "distribution velocity."
Hiring mistakes
That means you want to be careful when thinking hiring in general:
1/ First set of hiring mistakes often happen because you hire too early. Often, the business is not going the way you (or your investors) imagined, and you're being pushed into some hiring that should fix that. A sign that it's not ok might be that you do not naturally feel like you need or even want to hire. That's a bad start.
2/ Secondly, mistakes happen when your experience and knowledge do not come from a purely product-oriented startup environment but (oh my), for example, from a larger organization(s). Your inclination to solve things with "a process" and people who will manage it is understandable, but it's also very WRONG!
If you, as a founder or co-founder, can't keep your team on track towards building lovable product, no process or new person will.
3/ Don't hire junior roles unless you are comfortable with a lot of experimentation. I am still shocked at how many small companies have roles like Project manager, Junior marketing, or Junior sales manager. There's nothing you need a project manager for in a startup with less than approx. 1.000 people. And even then, it's only in particular business cases.
Also, you don't hire any junior people. The idea of a junior is that there's a senior he/she can learn from. If you want to turn your startup into learning & experimental ground for someone with limited experience, please don't downgrade them with a silly Junior title.
I am absolutely in favor of hiring for potential (at certain positions and situations), but then you have to go full in and let the person know you trust them to figure it all out, and you have to support their experiments and accept mistakes.
4/ Fourth, you don't wait for ideal hire! Because ideal hires don't happen. And if they do, it's just pure luck and coincidence. But that shouldn't stop you! I will explain what an ideal hire most-likely looks like in a moment.
Warning point - hiring an AGENCY (Sales/Marketing/PR/DevOps...etc.) WILL NOT SOLVE YOUR PROBLEMS, and you should never do it if unless have the core covered internally - and you just want to temporarily expand your capacity or knowledge in the certain area!
Agencies are great for helping with specific situations (not many of them, but some) - say a product launch, but if you have nobody internally to manage, learn and align your agency's effort it will be just money spent without long term benefits. See my previous essay on this topic.
How to hire better
So far, I've told you about mistakes I see all around. Why am I so negative today? I'm not negative; I want to prepare you for the fact that good hires can mean good things; wrong hires (or no hires) will inevitably mean not so ideal future. And that's not only with regards to money and time you've lost, but also opportunities lost to hire better, and imagine how many activities and bad decisions and wrong actions such a bad hire can do before you part ways. Yeah, horrifying, I know.
The best way to do hires in areas you don't understand and you've never hired for is to ask someone for help. Ask someone you trust who did hire for and understands these areas - maybe your investors, maybe your past boss. It's simply better to ask someone than trying to wing it.
Let me give you a recent example - it's from a hardware & software Web3 startup
They're building a hardware and software and they came up with the idea, that they need to hire some project manager(s) and a product manager to help them with growth. They already have over 20+ engineers and surprisingly also some Junior BD person and assistants and marketing. This is pretty tragic situation and setup.
As an engineering team you may need this extra two person team that can take you very almost to finish line!
This often happens to companies that were early in some area and lived + grew through the period of initial bull markets. They have winged most of the decissions and operations with almost total ignorance, yet it produced good results. Because there's a lack of experience, nobody can say if those results should be 10x or 100x better. They were good enough.
But the fact is that with any early stage startup, including hardware one, there's a 2 person combo you need that can take you very far - almost to finish line 
. You need that business-focused CBO (Chief Business Officer) and a marketing generalist MD who worked in hardware before and understands the grind. Even when it seems pretty obvious, they will tell you that you need to start visiting physical events as soon as possible because they add credibility to hardware startups like nothing else. And they will make sure you do all the work necessary before the events, at the events, and after them as well. It's a grind, like most things that work. They will also take care of managing whatever you thought were those "projects" and they will most likely re-shuffle your team and operations in a way that results get produced no matter what and faster and cheaper.
That's pretty much all you need until the demand for your products and services will go balistic!
There are small differences in roles in different verticals and between web2 and web3 but in general these rules are as true as they can be! Break them at your own peril 
I'm serious!
I hope you found something useful here and you will stick around!
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Find me as BFG (aka BrightFutureGuy) and let's connect!
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