In addition to Suthainn's list, if your GM allows, you can take the Ability Focus feat to boost the DC of one hex by 2 (I recommend Misfortune personally).
And while it may seem like a bit of a waste of a quickened ill omen, landing a misfortune right after to keep a boss locked down the rest of combat is amazing.
Statistically, rolling a natural 20 while misfortuned is 1 in 400 rather than 1 in 20, and rolling a 1 is approximately 1 in 10 rather than 1 in 20. That's where misfortune shines and why people think witches are so strong. Your party will thank you that the BBEG can no longer land attacks (unless they're hideously strong...which does happen in RotRL) and fails pretty much all of their saving throws the rest of combat.
If you're facing a boss with high will saves (usually discernible if you're facing a spell caster or with a quick knowledge check for other creatures), then take the turn to land an evil eye. Combined with an ill omen, your misfortune is pretty much guaranteed to land.
Mindless creatures do suck, but that's an issue that will mostly go away after book 2 of RotRL wraps up. There will always be fights from time to time with immunity to mind-affecting, but they're not so constant as they are in The Skinsaw Murders. In such situations, absolutely go back to blasting or using other forms of control. My witch LOVED a well placed web. Also remember as others have said, Misfortune is NOT mind-affecting!
If your party is 1-2 rounding boss battles, then your DM should probably tune the fights a bit higher for appropriate challenge levels.