Over the past two decades, I have been fortunate to work in major companies, medium-sized firms, and with my own Project Management consulting organization. As a business owner today, I have a clear idea of how I can go under: fail to deliver on the work I promised to my clients. In fact, small business owners must be on their toes all the time because our clients have little patience, and many will make a move to another company even when we fall short just once. In sum, when we do not meet expectations, we essentially fire ourselves!
When working in a company, getting the pink slip takes time, unless your mistake is a big one, such as theft or fraudulent acts. For the most part, though, employees can keep their jobs even if they are falling short of expectations. I understand that my comment is general in nature, and the industry will dictate how much rope the employer will allow the employee. For instance, I am certain that a car salesperson will be under the gun when failing to meet the monthly quotas.

#1: Do Only What is Expected, and Not Too Well
Too many people take their job descriptions too seriously. If an activity is not explicitly stated as part of their daily requirements, they will not even consider working on it. You will hear excuses such as, "Not for me!" and "Woah! I have enough work of my own!" In some cases, people will even tell you they are not qualified to do the extra work, even when they have no idea what is being asked of them. Interestingly, these individuals are usually mediocre in the work they do, but they know the system well, and will ratchet up their effort a month or so before performance appraisals. In management, this is known as the Recency Effect.
#2: Avoid Training Opportunities, and Complain When Compulsory
You can hear these workers already: "No, not again! This training is a waste of time. I will forget what I learned before I get to my desk!" The fact is that additional training keeps you sharp, and provides you with opportunities to learn more skills. I recommend seeking training and development classes outside of your employment. You can find excellent courses at affordable rates in your area. Before long, you will separate yourself from others, and that effort places you in the top 10% in your company. As the saying goes, Luck is what happens when opportunity meets preparedness.
#3: Tell Others You are Job Hunting, and Hope it Does Not Get Back to Your Boss
Of course, you know this is silly, but it does happen. When you accept a job offer, put 100% effort into the work. The job itself is not a long-term commitment for you, but your work ethic must come to the forefront. Even when hired to do work that you like, you will find aspects that are not exciting. By taking an approach that the work has to get done right, you will develop a positive and proactive attitude. In many cases, it is your "can-do" attitude that will help you advance in your career.
Interestingly, it isn't that easy to get fired from most jobs. You are likely to receive many chances to get yourself back on track. However, remember that you are not moving forward when trying to correct performance issues, meaning that you are falling behind. My experience is that you will receive more chances to improve from jobs that don't pay well, and these companies are mostly looking for warm bodies to handle routine work.
Therefore, get yourself on a track where you are accountable for performance. The pressure is more intense on this playing field, but the rewards are plentiful, and even exponential.