In Australia, the rules about vehicle registration will vary from state to state. However, in all states, it can mean a very expensive fine to drive an unregistered vehicle, so it's vital that you understand the details of registering your vehicle properly and the safety inspections it may need for registration. Note a few misconceptions people often have about vehicle registration in NSW, so you're sure to have your car always properly registered and legal to be on the road.
Your vehicle's registration lapses on midnight the evening of the expiry date; it doesn't lapse on that date itself, so if you've let your renewal run down to the last minute, you can still get a new registration on that day and be fine to drive. However, even being one day late with the renewal can mean a citation and fine if you're caught on the road.
Also, note that the registration is actually cancelled if you let it lapse for several months. In that case, you need to turn in the license plates for the vehicle, as it's illegal to have them in your possession when the registration has lapsed; this is true even if you're not using them, such as for a car that was totalled and you had towed to a scrap yard.
Individually constructed vehicles
Vehicles that have a modified chassis or frame are considered individually constructed, and these may need to pass additional inspections to ensure they're safe to be on the road. Don't assume that the modifications you performed on a vehicle aren't extensive enough to mean it needs a new inspection; if you're not sure what changes to a car would qualify it as being individually constructed, check with the office that handles registrations about the work you've done before driving it.
Selling the vehicle
If you want to sell the vehicle, you need to provide potential buyers with a safety inspection report that is not more than 42 days old; this is important to note, as you may have an older inspection that you used to get a registration. However, you don't want to assume that this older inspection would be valid for selling the vehicle. Be sure you check the date of the inspection report you have on hand, and have a new one performed for your vehicle if needed; this legally needs to be done before you even list it as being for sale, not after you have interest from buyers.