Appraoch towards asana practice session

Hi,

I have been practicing asana-pranayama for past 3 years…
My questions are based on my own experiences and mistakes I made in my approach towards practice session.

My question is how should we approach asana session so that
1.) we can progress continuously with the spirit of yoga
2.) dont become attached to/obsessed with any particular asana but at the same time dont give up also totally and finally succeed.
3.) keep asana session interesting and motivating.

Should we follow a fixed routine or should we try new things… Is it necessary to practice for fixed time daily… Cant I practice for 2 hrs one day if i feel like and other day i practice for 15 minutes only…

Right now I am practicing at home though I did learn under a teacher for 2 years. After some time I started finding routine class boring and so I started practicing on my own…