Aim for an ISO of 100 (or as low as possible) and a good rule is to set your shutter speed to x2 of your frame rate so in your case 1080P @60fps = 120 shutter speed
also as said above ND filters will definitely help:
When I first acquired my P3 Pro I was a little confused around how an ND filter could help with my videography until I came across this neat little explanation, I use this method all the time now and am very happy with the results I get when shooting video
Here is a good explanation for how to use an ND filter:
1) Take your phantom without a filter and raise it to a moderate height and hover
2) In your app, turn on the MANUAL exposure control
3) Set your ISO at 100
4) Set your shutter speed at 2x your frame rate
(4k @ 30fps = shutter speed of 60)
(1080P @ 50fps = shutter speed of 100)
(1080P @ 25fps = shutter speed of 50) and so on
5) Take a look at the EV rating at the bottom in the same window as your ISO and shutter speed settings...this will tell you approx. how many stops you need:
For example = if your EV says +1.7.........you need a 2-stop filter
if your EV says +2.1........ you need a 2-stop filter
if your EV says +3.2......... you need a 3-stop filter
if your EV says +3.9....... you need a 4-stop filter ....etc
Science behind filter number and stops: The science uses a base of 2 and you multiply the number of stops to get the filter number....i.e.:
ND2 = 1-stop
ND4 = 2-stops [i.e. 2*2 =4]
ND8 = 3-stops [i.e. 2*2*2 = 8)
ND16 = 4 stops [i.e. 2*2*2*2 = 16] ...etc
Hope this helps