For early rounds in which you can't get into your dream course put the early offer courses to give yourself a backup (if you're interested in them and have applied that is). If the early entry course requires having it as preference 1 for main round (many don't) you would have to take into consideration your mark and if you have a reasonable chance at your goal course. However most early entry courses take place in earlier rounds and once you get offered the place you can remove it from your list for later rounds and get more offers.
However for main rounds you want your preference list to be just that, a preference list. So whatever course you want to get into the very most should be at the top of your list; regardless of you thinking you will reach the ATAR or not. This would be similar to preference 2 in that you would choose a course you would really like to do and would be happy to get. Preferences 3, 4 and 5 should be your backup courses; still in order of preference to these but for the lower preferences you want to put something a little bit lower to serve as a backup if you don't reach your goal score. However once ATAR's are released you have an opportunity to change your list so can adjust it - however even if you don't actually reach the ATAR for preference 1 or 2; especially if reasonably close, DO NOT remove it from your list as the ATARs can change and you may get an offer. However in this case make sure you include reasonable backups in your later preferences for which you satisfy the requirements.
The way the system works is that you are given an offer to the highest item in your list for which you are eligible. But you only get 1 offer per round. So if you were to put a 70 ATAR course at the top when your dream course is actually a 90 ATAR you won't even be considered for the 90 ATAR course because you would be marked as completed as soon as they got you into the 70 ATAR course.
Hope this helps.