I've been offering freelancing consulting from over 4 years now, and it has been an amazing experience so far. I can perfectly remember the days when I first started where I would work for even 12 straight hours, seven days a week.
Today, I work less than 40 hours per week and my income has doubled. Not only that, but my income is also increasing constantly each month. I've learned a lot along the way, and below are the top five mistakes I was doing when I first started.
Working too much hours. The first mistake I made was working too much hours. Working 12 hours may seem productive while you're doing it, but it sucks up your resources and you end up being very tired after a few days. Instead of working all those hours, I learned to prioritize my tasks and focusing only on the important things first.
Focusing only on my core niche. I work on a very specific niche, and I'm very happy with that. However, it's important that you stay up to date and study other topics including personal development, productivity, and stuff related to your work.
Asking too little. When I first started freelancing, I was worried I was asking too much. The truth is that we are often asking too little instead. Your goal should be to ask a premium and provide the best quality possible for your services. Most clients prefer to pay a bit more but have a quality product rather than spending less but ending up with a mediocre service.
Having no passive income. Having a source of passive income is very important in those moments when it's hard to find new clients. How to set up passive income streams depends on what kind of freelancer you are. If you make websites for example, you could offer hosting or monthly maintenance.
Not having a public profile. Being known online is a must, and I would personally spend a large amount of time (after having done my work) working on my blog and building connections.
The Unlimited Freelancer is a book that helped me a lot building my freelancing business in the past months. You can read my review at http://www.theunlimitedfreelancer.net/.