Experts generally agree that startup businesses often fail because they run out of money too quickly before turning a profit. It's never a bad idea to overestimate the amount of startup capital you need, as it can be a while before the business begins to bring in sustainable revenue. Additionally, don't overspend when starting a business. Understand the types of purchases that make sense for your business and avoid overspending on fancy new equipment that won't help you reach your business goals.
Don't sacrifice morals for a quick buck — At the outset, you'll want to do all sorts of things to make money online, but don't sacrifice your morals for a quick buck. Not only will you put people off, but you'll lose Google's trust. You also shouldn't concern yourself with things like Adsense or other ads on a blog before you have around 100,000 visitors per day. Yes, per day.
Double check yourself, before you double wreck yourself. Make sure everything you send to a company, whether a résumé, an email or a portfolio, is good to go. Double check your grammar and wording, and for God’s sake use spell check! This is especially important when it comes to the company’s name. Don’t spell their name wrong and be sure to type it how they type it (e.g. Problogger, not Pro Blogger).