I have like 30 different photos to process like this, but I want to know key things to maintain realistic photo by changing it's background, or maybe just modify background so it would be more pleasing to eye.(If you know tutorial related to my problem, please do provide it to me)
Here is the photo:
Here is my step 2:
Here is background:
Here is the result:
As you can see, it isn't any close to realistic feel. I fooled around with levels, but all I got was this and still it doesn't feels right.