Look at your plate and on it will be a year/month stickers. The month is the one you need to get a new sticker. I don't know about other states but in CA a notice/bill is sent to the owner of the car about 6 weeks before it expires.
a license plate
can i renew my license plate sticker for 6 months
License plate sticker showing the year and month of expiration for a vehicle are obtained from your local motor vehicle office upon successful renewal of your annual auto registration fee.Any driving test places
The color of the license plate sticker depends on the state in which you obtained the vehicle license.
michigan plate and sticker
The registration sticker goes only on the back Ohio state license plate. The front plate has no sticker. The new sticker should be placed directly over the last sticker in the lower right corner.
usually on your birthday
the rear plate
In Connecticut we don't use the registration sticker on the license plates any more but when we did the sticker went on the rear license plate.
Depending on where you live it may be different but typically there should be a sticker on you license plate that will indicate when you should renew it.
If you're asking about where to put your sticker on the license plate than that would be the rear plate.
the top right corner