This is a re-post from @JonSmith as a sticky for reference:
Greater Than ex: LastUpdated => ‘~>~ 2017-01-01 00:00:00’
Greater Than or Equal to ex: LastUpdated => ‘~>=~ 2017-01-01 00:00:00’
Less Than ex: LastUpdated => ‘~<~ 2017-01-01 00:00:00’
Less Than or Equal to ex: LastUpdated => ‘~<=~ 2017-01-01 00:00:00’
Not Equal to ex: Id => ‘~<>~123’
Is Null ex: FirstName => ‘~null~’
IN statement ex: Id => [1,2,3,4]**
*The raw xml, will need be html encoded for ‘>’ and ‘<’
**IN statements only work on Id fields and are limited to 1000 ids