I recently bought LG G3 and I have enabled debugging mode but Eclipse is still not recognizing it, back when I used the Galaxy S3 for development I had to install Samsung Ki
Right click on My Computer --> Properties --> Device Manager
Right Click on your device --> Update driver software
Click on "Browse my computer for driver software"
Give path of your android sdk like "D:\Android_Sdk\sdk\extras\google\usb_driver" and tick "Include subfolders"
Click
Now repeat the steps till "Browse my computer for driver software".
Then click on "Let me pick form list of device drivers on my computer". Click on the first option and click next and then click yes. Drivers will be installed for your device.