Does 'installation unsucessful' apps occupy space in SD card After downloading some of the apps from google store I get a notification stating phone memory low and subsequently the installation gets failed.My question does these not installed app files get stored somewhere in my SD card and occupy any space?If yes,how can I delete these files.
You can install the diskusage app toy our phone to see what is consuming the most disk usage and if you can free it up. It is a free app, and is only 155kb in size. 

I would also recommend ES file manager, but it is a few mb in size. But it allows you to view all the directories on your SD card. 

Finally, get dropbox or google+, they will backup your photos over wifi, so you can delete them from your phone to save space.