Hope someone can help. I'm traveling on Qantas from Johannesburg South Africa arriving in Sydney at 14h45 T1, then need to transfer to T3 to catch a connecting Qantas flight to Melbourne departing at 16h15 - only 90 minute layover. Any advice to ensure I don't miss my connecting flight to Melbourne?

When I return to Johannesburg I depart Melbourne, arriving in Sydney T3 at 09h35 and need to catch my connecting flight departing at 10h35. My bags will be checked in straight to Johannesburg from Melbourne. Again, any advice?

I guess what I really need are some directions around the airport so that I don't waste time getting lost.