establish a routine and make sure it starts and ends at the same time everyday, for example sit down at 1 and study till 4pm every day.
write down a list of what you have to do during a holidays, then make a calendar of what you will do each day. for example - notes on climate variation on 12/07, 2 trials papers 13/07, etc.
give yourself dedicated leisure time, but give yourself a time limit for it (unless you have no more work to complete that day). for example, i can play video games from 10-11 am, but then i have to study from 12 - 4, and can only play once ive finished my work for the day.
try do work in the morning or midday. you tend to be more motivated during that time, then once youre done you can do whatever.