A lot of people skip the very first step of FINDING people when they answer this question. Before you can offer free consultations, or ask for referrals, you need to find the right people, who have the right problem.
For this, you generally have to start with some manual marketing... search online (reddit, forums, blogs, etc) for questions that people may ask, pertaining to your consulting business' niche. From there, you insert yourself within the space, answer questions, offer solutions, offer your services, and in many cases, even directly reach out to online users that you think would benefit from your service.
Another way, if you have money to invest, is to pay for advertising. This can be as little as 1 dollar on a Facebook and/or Instagram ad, or as much millions of dollars for a tv advertisement.
There are many many many platforms out there for you to advertise on at varying prices. For a consulting business, cheap Facebook ads targeting businesses, locations, interests and behaviours of customers in your niche is a great way to go. You should have a Facebook & Instagram page for your business, so you can use FB's Lead Generation campaign oriented advertisements in the FB Business Manager to have interested impressions (people that are interested in your service after seeing your ad) input their information into a form, so that you can proactively follow up with email, by phone, etc.
In conclusion, manual marketing, and sensible advertising at a budget you can afford. It sounds simple, but there are many different ways you can do this for different industries and niches.