There isn't much to do here. Your current check is syntactically correct, but may not be practical. Why do you care if space utilization is greater than 10%??!?
A typical disk check stanza would look like:
check device var with path /var
if SPACE usage > 80% then alert
That basically will send an email if the drive is more than 80% full. Monit will also let you know once the data usage falls below that level. Also look at the Monit documentation.
monit status at the command line. Here's what Monit sees about your filesytem:
monitoring status Monitored
filesystem flags 0x400
block size 4096 B
blocks total 1523090 [5949.6 MB]
blocks free for non superuser 979860 [3827.6 MB] [64.3%]
blocks free total 1058477 [4134.7 MB] [69.5%]
inodes total 1572864
inodes free 1563392 [99.4%]
data collected Sat, 03 Aug 2013 22:07:28