1
I'm tired after working all day.
Point to yourself for 'I', then place your bent hands on your chest and let them drop downward for 'tired', making sure your face looks exhausted to match the feeling.
2
I'm tired, so I am going to bed.
Start by pointing to your chest with your index finger. Then, bring both bent hands to your chest and pivot them downward, letting your shoulders slump slightly to emphasize your fatigue.
3
Sorry, I can't go. I'm tired.
After signing 'sorry', point to yourself. Then, execute the 'tired' sign by resting your bent hands on your chest and rolling them downward, using a weary facial expression.