If you insist on using ladder, only use them if the window is within easy reach DO NOT try for the window that is difficult to reach.
Do not rush, at first you will find it could be taking you an hour to clean 1 house, don't worry about it and do not try to increase you speed, when you get more practice you speed will creep up, don't force it.
Invest in a unger pole, you can use this on some 3rd storey work, you will not get a perfect finsh but at least you will be alive for you finals.
The rest is experence, you have 10 days before you start on you first fee paying customer, so for the next days and nights, practice then practice then practice some more, clean the windows at your sudent digs and parents home and any other window you can get to clean, and kept on cleaning them, you will be able to see what the results are from the inside.
Also for many newbies the first mistake they make is the price, find out what the local windies are charging and match it.