Niyamas are the guidelines personal observances. Compared with the yamas, the niyamas are more personal. They refer to the attitude we adopt toward ourselves.
1. Sauca - Purity
Outer cleanliness is pretty self explanatory whereas Inner cleanliness means healthy bodily organs and clarity of mind (we're looking at you: cigarettes and booze!). Practicing asanas or pranayama are essential means for attending to this inner sauca. Asana can help tone the body and remove toxins while pranayama cleanses our lungs, oxygenates our blood and purifies our nerves.
You might also consider 'cleansing' the mind of negative emotions like hatred and greed.
2. Santosa - Contentment
Santosa refers being content with what we have, being happy with what we have rather than being unhappy about what we don't have.
3. Tapas – Disciplined use of our energy
Tapas refers to the activity of harnessing inner urges (like the desire to lay in bed all day and eat chocolate cake... I've been there...). Behind the notion of tapas lies the idea we can direct our energy to enthusiastically engage life and achieve our ultimate goal of creating union with the Divine. Attention to body posture, attention to eating habits, attention to breathing patterns - these are all tapas.
4. Svadhyaya – Self study
The fourth niyama is svadhyaya. Sva means "self' adhyaya means "inquiry" or "examination". Any activity that cultivates self-reflective consciousness can be considered svadhyaya. It means to intentionally find self-awareness in all our activities and efforts.
5. Isvarapranidhana - Celebration of the Spiritual
Isvarapranidhana means "to lay all your actions at the feet of God." Relating to an idea (and celebration of such) that there are forces larger than ourselves that guide and direct the course of our lives.