Not directly MMA related, but an optimistic mindset and enthusiasm will definitely help with the grind of training and pre-fight nerves.
Positive Self Talk
Have a mantra such as “Cool, calm & collected”
Here‘s a list of other possible mantras
Positive Room Entrance
Each time that you walk into a room, pick out 2 things you like and think about why. Make it as random & obscure as possible.
Remember a Happy Memory
You can’t think both positive & negative at the same time. Recall a time that you were really happy to improve your mood.
Smile & Breathe Deeply
Works best if you are anxious in my own experience. Anxiety is a survival response – you wouldn’t smile and breathe deeply if your live was in danger – thus the body provides feedback that all must be well and there’s no need to worry.