Here, I'll list a few basic things that any entrepreneur should take care of when starting a business, or at least find someone to help them do it.
A professional web site
This first one might be pretty obvious, but any business in this day and age needs a web site. Gone are the days of the yellow pages, and if someone can't refer to your site in order to find out what it is you do, then you have major problems. But what kind of site you need depends greatly on the kind of business you run. A lot of startups miss the bullseye when it comes to having a proper web site.
For example, if you run a law office, or a dentistry, then you probably don't need a big web site. You should get a simple portal that shows off who you are, what services you offer, what your hours are, and how to contact you. There's no need for a massive infrastructure, since the most interaction you may have on your site is a "contact me" form.
If you run an online store, then you need to decide whether you want to build your own storefront or use a site like Shopify or even just the Amazon Marketplace. This includes finding out how you're going to accept online payments, which could be as simple as setting up a PayPal.me page, which allows anyone to send money to your business as long as they have a credit card, or you may have a more complex system linked to your bank.
If you're more in the content business, maybe you just need a WordPress site. You may want to produce blog posts and keep people updated on the things you do. There's also a lot of alternatives like Blogger, Medium and so on, but whatever you choose, make sure you get a custom domain, so that people identify the site as being your own business.
A professional email address
This is something a lot of people forget. There's a huge difference in how professional you look if they can send you emails to email@example.com instead of firstname.lastname@example.org. The sad thing is most web hosts don't offer this type of email account, even though it's very simple to create a redirect, from the professional looking email to your own personal email account, and is something we do all the time.
If you have a more complex need, you may go for an entire Office 365 or Google Apps subscription, which gives you not only a professional email account, but also things like cloud storage and office applications. Determining your needs here is going to be important.
Social media presence
It doesn't matter whether you're purely an offline store, or a fully online business, having a social media presence is crucial these days. The best would be if you or one of your team member could post on a regular basis, to make a personal connection with your potential clients, but even just having someone monitor the accounts is important. People expect to be able to tweet to companies, and sites like LinkedIn are crucial to making professional connections.
Also, make sure you spend a few minutes making your profiles look the way you want them to look. Having the same handle on Facebook, Twitter, Instagram and so on is a good idea, that way people know how to reach you regardless of the platform. Also make sure you set a profile picture, contact information, and so on.
Unless your business is run and operated just by yourself, you need collaboration tools. And even if that's the case, there's plenty of occasions when you may want to communicate with a client, subcontractor or professional contact over text or video. Having a Slack, Zoom, Microsoft Team or Google Hangout account setup is important so you can share how to reach you with those who need to.
Once you have these few basic tools, you're set on the online front. Of course, depending on the type of business you run, you may have bigger needs. Maybe you want to offer your team members with free online courses at Skillshare or Udemy. Maybe you need to join some professional associations. Maybe you do development work and you need Microsoft Visual Studio or Amazon AWS subscriptions. Whatever the case is, starting with the basics means that you at least project a professional online profile for clients and business contacts alike.