1
His behavior in class was excellent.
To sign this, you would use the side-to-side sweeping 'B' hands for 'behavior', followed by the signs for 'class' and 'excellent'. Make sure to use a positive facial expression to emphasize that the conduct was good.
2
I need to change my behavior.
Start by pointing to yourself for 'I', sign 'need' and 'change', then transition smoothly into the flat 'B' handshapes moving side to side for 'behavior'. A serious or determined facial expression fits well here.
3
The dog's behavior is improving.
Sign 'dog', then use the sweeping 'B' hands for 'behavior', and finish with the sign for 'improve'. This shows that the sign isn't just for humans; it works perfectly for animal conduct as well.