Sezza - there are no "tricks' but definitely tips

Basically spending 2 hours 4 days a week and 4 hours on weekends got me approx 50 points per month. I went from 540 to 750 in 3-4 months.
Of course it is easier to improve from 500 to 600 than from 600 to 700 or 700 to 800, so potentially you can make 100 point leap but I would say it would be hard/very hard to get there if have already studied for 3 months and got 500.
You may need to change your study pattern - possibly study in the morning or study in a locked room/airplane/hotel room - somewhere where you are not distracted and can spend a few hours uninterrupted. You also need an
error log and spend a lot of time reviewing your results.
Basically, unless you are shooting for 600, you will be wasting your money and should move the date. If not, spend time on the area you feel can be improved the easiest.
P.S. I thought you said your exam was on the 29th of June? Did you change it?