These are my top three mindset changes that are simple to adopt right now. These simple practices will result in positive mental benefits. The suggestions work with your bodies hard-wiring and can train you in healthy ways to think.

Gratitude:

There are things in your life now that you used to long to have; a partner, a house, children, a car, income, hobbies. When the novel becomes familiar it can lose its power to fill us with the contentment we seek. Gratitude is one way to focus your mind on thoughts that promote pleasure and peace.
Try this simple tool:

Make a list of 10 things right now you are grateful for. Spend a few seconds with each thing on your list. Focus on how good these things are for you and notice the emotional shift in your body. See if just reflecting and being grateful can bring a smile to your face. This takes 3 minutes.

Pause:

Your mind can focus well for about 20 minutes at a time. Regular pauses in your day mean that you are optimising your brains performance. See if you can take a pause after reading this article. Choose from this list of simple pause moments: 
Stare out of the window and notice what is outside.
Get up and walk around the room making your breathing slow and deliberate.
Remember your favourite song and play it all the way through in your mind.
Choose a small, healthy piece of food (a handful of raisins, a slice of apple, carrot stick). Eat it slowly noticing how it tastes and enjoying it.

Pleasure:

Do you know what you enjoy? When your brain experiences pleasure it releases serotonin. This hormone is (in part) responsible for the brain's ability to learn. Its why you feel refreshed after a good night’s sleep. Doing more of what you enjoy will cause your brain to be better at taking on new information. A friend of mine enjoys being outside and has adapted his regular tasks so he can do them outside. Can you be more strategic and intentional about the pleasure in your life? Find one thing pleasurable to do today.