Philippians 4:8 Finally, brethren, whatever things are true, whatever things are noble, whatever things are just, whatever things are pure, whatever things are lovely, whatever things are of good report, if there is any virtue and if there is anything praiseworthy—meditate on these things.

The bible give prescription on what you are supposed to be thinking about, don't just accept any kind of thoughts that comes. You must be deliberate about what you allow in your mind.  The scripture above tells us things that are expected of us to think about. Your joy can be affected by negative thoughts. 

You need to understand that the enemy wants to hijack your thoughts and imagination, use the same against you. You must deliberately guard your mind. God gave you ability to think and imagine, but Satan wants it corrupted with negative thoughts and pictures. You must be careful of what you costume through the gateway of your eyes. 

Matthew 6:22 “The lamp of the body is the eye. If therefore your eye is good, your whole body will be full of light. 23 But if your eye is bad, your whole body will be full of darkness. If therefore the light that is in you is darkness, how great is that darkness!

Make up your mind to be selective of what you hear, watch, touch etc. God has a great plan for you, but the purity of your mind is as important as the plans He has for you. 

Olanrewaju Niyi