Emirates offers an online check-in service for flights departing from 110 airports, including Dubai, London Gatwick and London Heathrow. However, you can't check in online if your first flight is being operated by another airline, even if it's a codeshare flight. If the first flight on your itinerary is with Qantas Airways, however, you can use the Qantas online check-in service instead.
To use the Emirates online check-in service, you'll need your booking reference/PNR and the surnames of anyone you want to check in. You can check in up to nine passengers if they're on the same booking and you can change your seats at this stage. Anyone aged under 16 who is travelling without an adult cannot check in online.
Once you've checked in, unless further checks are required, you'll be sent an e-boarding pass. If you can't print this, you can take your passport and ticket to the Emirates desk at the airport and inform the staff that you've checked in online. If further document checks are necessary, you'll need to collect your boarding pass from the airport's Emirates desk.
The online check-in system will be open from 48 hours until 90 minutes before your flight's departure time. You'll need to arrive at the airport at least an hour before your flight departs if you aren't checking baggage in, and at least 90 minutes before departure time if you are. Once there, follow the instructions on your boarding pass.