The question of HM gear comes up often, so I'd like to put these basic requirements out there. These are for DF/DP, since those are where we send our HM groups.
Absolute Minimum HM Gear:
Basic Gear: All armoring, hilts, barrels, mods and enhancements 168, with the exception of your off hand, please have your Oriconian offhand. ALSO, please check your stats. Comm gear very often sneaks some stats in that you don't want. Examples: Tanks gear sometimes has alacrity, some sets of healing gear are all crit.
Set Items: Exception to above rule, have at least your 2 piece set bonus, even if you use Arkanian armoring to get it. Obviously, keep hitting the SM Ops to upgrade to Underworld ASAP.
Implants and Earpiece: Oriconian, unless a lower level is demonstrably better for your spec (i think tanks have said a crafted one is better for them)
Relics: Obroan. Very, VERY easy to get with just a little PVP and they're the third best available in game.
Augments: Here's the expensive part. Full augments, every single piece, rating 156, those are the sexy purple ones. Ask around the guild to find crafters, so you get a better price than GTN. Note: Everyone but tanks should start with main stat augments, check Ioniafi's reply below for reasons. Tanks, you have a slightly longer process to decide which augments to use. Check this link! http://www.violentbydesign.org/tankstats.php
Some other considerations: (consider these strong suggestions)
Needed on your action bar:
Aggro Dump - Unless you're a tank, you need this readily available.
Cleanse/self-cleanse - Most classes have one or the other, some have both. If your class has them, you need it easily accessible. Powertech, Juggernaut, and marauder get neither.
Interrupt: Everybody's got one, have it ready.
Interface changes:
Target of Target: Turn this on in the interface editor.
Target castbar and focus target castbar: also in interface editor.
Buffs and Debuffs: In the interface editor, edit your ops frame and turn down the size of buffs to 0.15, and increase debuff size to 0.6 (0.5 is okay, 0.6 seems better for Dread Council)
Failing to Prepare is the same as Preparing to Fail:
Before going into a Harm Mode operation, check out some videos to get familiar with the fights. I highly recommend Dulfy videos, since she makes annotations of each thing to know about the fights.
Mentality:
In SM Operations, it's all abut getting the weekly and clearing the Op. HM and NM are far different animals. In those tiers, it's all about clearing individual bosses. You may bash your head against a single boss 10 or more times before you get it down.
Supplies:
Stims: You'll need the appropriate stim for your class/role, the reusables are 'okay', but honestly, the blue quality ones give a bigger boost, so are much preferred.
Medpacs: Again, reusables are only okay. Blue quality medpacs heal more, and apply a HoT, so those are the ones you want.
Adrenals: Bring a few stacks of these, as you might get a chance to use two in longer fights. Again, same situation as the other medical supplies, reusables aren't the best.
Credits: You're going to die. A lot. So, be ready for repair expenses, around 5k per death, so bring a few hundred thousand credits just to be ready.
