A good advisor can help a startup in various ways. Here I describe what I do:

I work quite a bit with pre-angel/pre-seed/pre-accelerator US-based tech startups (or sometimes even executives/scientists/technologists in corporate jobs toying with a startup idea that they'd consider leaving their jobs for), and have done this now for well over a decade while founding/growing my own companies. Most of these founders come to me from hearing about me from another founder, so I am assuming that founders are finding some value in their interactions with me.

At this early-stage in the game, one of the key things I try to do is to separate founders' assumptions about various aspects of the business from facts that they have validated. Another thing founders find useful is examples/ideas of how other startups solved a similar business problem in a creative manner (my voracious reading helps a lot here.) Finally, I also try to take the devil's advocate position on key assertions that the founders make (e.g. why are they & their product uniquely suited to tackle this problem in face of competition) in order to point out counterarguments with the eventual goal of helping them strengthen their case.

My engagements with founders tend to take the form of intense 30-75 minute brainstorming sessions (1-3 sessions), which typically provide them with enough food for thought to start executing on various fronts.

A small percentage of these startups continue to make great progress over a period of 3-9 months and keep me in the loop via brief email updates. Those ones, I help by providing them critical feedback on their pitch decks (multiple iterations until I think that it is crisp and powerful) and then bring on the radars of my early-stage investor contacts (US-based).

There are of course different advisers... Technical (scientific) and business. One of the big add value from a good advisor is their name and connections in the field. That adds lots of credibility to a startup and help with discussions and negotiations.

Good advisors bring a lot of things to the table. Let us take an example. You have created a Start-up almost a year ago i.e. in 2019, now during coronavirus pandemic you are facing a financial crisis and you need a financial advisor. A good financial advisor that you will hire will bring the following traits to the table and if they do not, they are simply not good.
1. Passion for Financial Planning and Wealth Management: The successful financial advisors are the ones who have an absolute passion for the subject. This is important because standards, laws, methodologies, and products within the financial and investment worlds are constantly evolving. When a financial advisor has a huge passion for the subject matter, that person naturally gravitates toward learning more and more about the industry every day. Those without that passion consistently fall behind and struggle to keep up with industry developments. That alone can be the difference between success and failure as a financial advisor. A good question to ask financial advisors with every conversation is, "What's new in the industry?"
2. Deep Analytical Ability: There are many areas involved in a complete and thorough financial plan. Cash flow planning, retirement planning, investment management, insurance planning, estate planning, and tax planning are a few key areas that a competent financial advisor can help clients with. Having in-depth analytical ability across all these areas is essential, but it is perhaps most important in the investing portion. Successful financial advisors know that the risk and return relationship drives almost every aspect of a financial plan. Structuring an investment portfolio, the proper way and being able to reallocate the assets as time and goals change is crucial. A financial advisor needs to be able to analyse and plan a portfolio in the context of a variety of metrics, such as standard deviation, beta, strategic asset allocation, tactical asset allocation, and drawdown.
3. Professional Salesmanship: This is a key requirement for successful financial advisors. Financial advisors must grow their book of business to thrive. Being able to sell their services across the entire spectrum of financial planning, from investment management to estate planning, is necessary for financial advisors to be successful. Granted, sales of services or products should not be made solely to make a sale. The service or product must genuinely help the client. However, salesmanship nonetheless is necessary. A financial advisor must be able to communicate to the client the problem or gap in his or her financial plan that exists, properly convey the solution, and as a final step, ask for the client's or prospect's business. A financial advisor who cannot muster up the courage to ask for business will undoubtedly get none. The next trait is crucial.
4. A Belief That Interests Must Be Aligned: Successful financial advisors are ones that put the interests of their clients first and their own interests second. The advisor must believe that the financial interests of both parties should be aligned, or else a harmful relationship may occur. It is unnecessary and unethical to sell a client product that the client does not need, such as irrelevant insurance policies or insurance policies with too much coverage. Certain investment products fit this category as well, such as mutual funds that have high sales loads, since there are countless comparable and better mutual funds without such loads. In addition, charging higher-than-necessary investment management fees is not good practice. A successful financial advisor should not charge 2% on assets under management when 0.5% is typical for the same service. Successful financial advisors help people and are compensated fairly; they do not drain their clients of their hard-earned money.
5. Curiosity: Uncovering precisely what a client needs across all aspects of financial planning is like detective work. Small details must be found and pieced together, and a comprehensive solution to a large problem must be created and communicated. Successful financial advisors are ones who enjoy this process and thrive on the challenge.
Besides if you do have any questions give me a call: https://clarity.fm/joy-brotonath