My mobile phone's internal memory is almost full. So I inserted a 8GB micro SD card in it and set storage settings to SD card. I tried to download some apps from Google play store to my phone but an Error message appears stating 'insufficient storage available' and couldn't succeeded in downloading. What to do?

Some apps will not operate from storage and the download folder is located on the local storage.
Time for a serious clear out.

Also did you format the SD card for the phone to use?

Also did you format the SD card for the phone to use?
Is it necessary to format brand new SD card? If yes, will you please explain the procedure of formatting?

What model of phone is it? Some do require formatting inorder to use them.

What model of phone is it? Some do require formatting inorder to use them.
My phone model : Micromax A58

From what Im seeing you need a GSM sim card.



SIM
Dual GSM+GSM MICROMAX A58 (http://inshopee.com/index.php?route=product/product&product_id=377)