As a rule you can begin by doing any Asana of your choice. But there are some Asanas which are to be followed by a particular Asana.
1. In the beginning Savasan should be done.
2. After doing Asanas, Savasan must be done.
3. After doing Paschimottana Asana, Chakrasan must be performed.
4. Ustrasan must be done after Halasan.
5. Matsyasan must be done after Sarvangasan.
6. Salabhasan must be done after Bhujangasan.
7. Tadasan must be done after Sirshasan.