How to avoid forgetting the things ,for ex..my car key, mobile,etc?

If you tend to be forgetful, doing two things will help a lot. First be organized. Choose a particular location for each of your things and put them in the same place everyday. Next, don't just put down something and rush off. Remind yourself once of what you did, like "I put my key in the top drawer" or "I put my mobile on my study table".

Trying to find our things is frustrating. Sometimes a work which can be done in a few minutes takes hours because we waste time searching for what we need.

Oh I sometimes forget things too. One time, I was screaming around for my pen and it was in my pocket. -.- Happens ALL the time and then I blame my pen or pencil of playing hide and seek. But for things like keys and such, you should get like a reminder thing, and set it to remind you every morning or when you know you are going to go somewhere, set the reminder to remind you at the time and you probably won't forget but I doubt my suggestion will completely work. Goody luck :)