Yoga is a Scientific System of physical and mental excellence which requires obedience to certain rules, principle and methodology in order to acquire satisfactory results. If these rules and principles are not followed it may cause reverse results, i.e. harm and injury to the body. 

1. There is no specific time for doing yoga. In the point of view of convenience, morning is always better as you will be free for the rest of the day. 
   Whatever time you have chosen, stick to the same time of practice every day. 
   Practice yoga regularly and continuously. Irregular practice will not bring good results. 
   Practice only once within twenty four hours. 
   Practice at least 15 minutes a day , for 5 days a week. 15 minutes can be gradually increased to a maximum of 1 hour. 
2. The place of yoga practice should be neat, clean and airy. 
   Try to practice at the same place regularly. 
   Practice alone, if possible. 
3. Yoga should be practiced on an empty stomach. 
   If you have taken food, wait for two or more hours before practicing. 
   Practitioner must avoid hot food or excessive spices and try to eat a balanced diet. 
4. Relax in between asanas for 6 to 8 seconds. Take 2 or 3 normal breaths between asanas. 
   Rest at the end of the asana session. The general principle is to rest ¹/₄^th of the time of actual practice. For example if you practice asanas for 30 minutes, your rest time is 7¹/₂ minutes.
5. Your body should be neat and clean nor it should be tired or under any excessive physical pain. 
   Wear clean and light cloth while practicing.  
   Avoid excessive intake of coffee, tea, alcohol and drugs. 
6. Try to keep the mind free from anxiety, worries and any strenuous involvement while you are practicing.
7. Women should not practice yoga during their menstrual periods. Pregnant women should take care to practice moderately.