Your mental approach should be proper regarding both your training schedule and performance schedule. Similarly you should psychologically motivate yourself to training sessions as much as to playing sessions.
Stage 1 is commitment. Unless you commit yourself mentally and not just physically, you are not going to enjoy the fruits of success. It is the first and foremost quality required for you to perform, let alone excel. Commitment should be intense for both training and playing.
Stage 2 is goal setting. You must have clear cut goals regarding your fitness level and playing proficiency. You must list out your weaknesses in your fitness schedule and game, be it an exercise regimen or a drop, smash, serving close to the net or whatever else it may be. Specific attention has to be paid to strengthen these areas.
Stage 3 is maintaining a positive attitude. Two negatives make a positive only in mathematics. In sports, two negatives make you next to nothing. Your speech, attitude, mannerisms, on and off court behavior should all exude confidence which others should perceive and comment about.
Stage 4 is feeling good about what you are doing. You must learn to enjoy your training and playing schedules. To put it very simple, a player should feel playing badminton as an enjoyable hobby rather than an unavoidable routine. When you really feel good about playing badminton, even the most challenging of shots can be executed with such fluency to keep you surprised enough.
Stage 5 is believing in your performance. If you don't believe in yourself, no one else is going to. Remember, not everyone in badminton started as world number one right from their first match. They started from nowhere, believed in their performance match after match, day after day whether they lost or won. And finally one day, they found themselves in the top. Unless they believe in their performance, they could not have scaled those heights.
Stage 6 is developing the knowledge regarding badminton. Look around all the legends past and present. Watch their games, either in television or in person. See how they tackle specific match situations. Imbibe their methods. Try it for yourself. If possible, talk to senior players, coaches and learn how to cope up with different game plans and training schedules. If possible, persuade them to watch you play and ask them to point out your weaknesses. It is very essential for you to have the knowledge of your weaknesses as much as the opponents' for you to play better badminton.
Stage 7 is concentrating on the basic aspects of the game. Remember, how much ever high the bird fly, it has to come to the ground for food and drink. Similarly, you must always concentrate on the basic aspects of the game even after becoming proficient in it. That way, you can keep your feet planted firmly to the ground while reaching for the skies with your hands. Good luck and happy playing.