Our ability to learn depends on our mood and mental state.
So how can we improve it?
Get enough sleep
Well rested brain responds faster and its retention ability is noticeably better
Sleep is extremely important for several reasons, but for this purpose I would like to point out just two: firstly, brain uses sleep for sorting and storing information and experience from the day (so that we have space for new ones the following day) and secondly, sleep has links to several brain functions, including concentration, productivity and cognition. That means that your ability to think lucidly is significantly limited when you are tired. The adequate sleep time for an adult is, according to studies, at least seven hours per night.
Quality of sleep is just as important as its duration
The ideal sleep environment is cool, quiet, and dark. You should also pay attention to quality of your matress, comfortable bed always enhances sleep. Apart from that try to avoid light from computers or phonescreens close to bedtime.
Meditate
Meditation is the habitual process of training your mind to focus and redirect your thoughts. You can use it to increase awareness of yourself and your surroundings. Many people think of it as a way to reduce stress and develop concentration.
If you do not know how to start, you can use some advice from the more experienced people. For example choose from abundance of apps that have been made for this purpose.
Believe in yourself
If you want to be successful in whatever you do, you firstly need to believe that you are capable of accomplishing it. One thing I would like to emphasize is that everything is possible and you can do it.
Exercise
Exercising should be part of your everyday life, but is even more important when it comes to studying. From boosting your energy and releasing stress levels to improving mood, memory and staying fit... it has a lot to offer. What is more, it can help you relax and sleep better. You can choose any type of sport including yoga, cycling, nordic walking, swimming or something more casual such as running or weight lifting. List of convenient activities is endless so there simply isn't any reason to deprive yourself of this experience :).
Change activities/ study topics
Doing same activity for long period of time can lead to boredom and loss of interest. Switching from biology to chemistry for instance can intensify curiosity and help you stay motivated. So try to alternate one topic with another or just take a short break in form of reading few pages of a fiction book. Use whatever you like!