Cut your hours.
At first glance, many creative professionals are horrified at this idea. It appears counter intuitive to cut your hours in order to get more done, but this is a proven successful method. It is easy to feel overwhelmed when you overload yourself with work, and you will find yourself dragging. This can lead to poorer work quality. By keeping your hours short, however, you can be more efficient and focus on the task at hand, rather than how much more you have to do.

Give your designs time to settle.
This will give your brain a break after hours of working on a project, and let you look at it with new clarity. You should always take a break before editing and making final adjustments. Many designers put together design portfolios and then put them aside for a few days before making them official.

Be aware of your energy levels.
When you have a lot of energy, put it into designing. When you know you have low energy, don't waste time trying to force yourself. Many people are more productive in the morning, while others find the most energy in the evening.

Be open to inspiration!
Inspiration can dome from anywhere, including other designer's portfolios online, a poster, a picture, or a person. Be ready to take advantage when inspiration strikes.

Listen to music.
This can be a great tool to use, when used properly.  Don't listen to music that will distract you, instead find something that keeps you focused.  Many creative professionals claim that fast paced music keeps them working at maximum productivity.