Before any Ops, need gear and able to do HMs. As said, HMs easier to get together for and I always say, shouldn't require special time to do them. But a definite time/night yeah

AND very fun! IF you dont mind possibly dying a few times

Remember, once you complete a HM FP you're locked out of that specific FP for 24 hours/daily reset. So you can't do False Emperor twice in one day for example.
MAJOR SUGGESTIONS: based on Kall, Sitilla (Nob), Cell and I doing a bit...
HM need pretty much a set order of roles: 1 Full spec Healer, 1 Tank, and 2 DPS. Wont get away with 2 tank specs 1 DPS and Healer imo... or 2 Healers 1 DPS 1 Tank. Certainly can try
Healers should expect a lot of aggro, Tanks be mobile, get aggro on you, first to hit any target and expect to be hit a lot

. DPS - just pew pew fast as can

Interrupts/CC too be vital for you to do.
GEAR: You really should to run a few Dailys you get on Illum/Belsavis Bonus AFTER completing class quest for the epic armor/barrel/hilt mods. They are 8 daily comms per mod, and also will receive some quest rewards that are enhancement/mods. Getting you weapon modded first, then a few armor mods is fine, can do that in one day. Not a requirement but will help a lot. Running the HMs will help your gear the most ultimately with it's drops, so long as rest of group is good with gear should be fine if you're new to 50.
Someone who knows the FP and the bosses will make things run a lot smoother and quicker - they aren't all tank and spank... all bosses have enrage timer, which you don't want to go off, because if it does, you = dead

(Boss 1-2 hits everyone) So maxing DPS is important, but interrupting and knowing any tricks needed to kill boss is just as vital.
Here's a rundown of HM FPs that we've won multiple times, in my order of easiest (in my opinion)...
1. Kaon - (maybe not if it's your first time, esp as tank/healer, because a lot of swarming mobs and special mobs that do annoying things) Drops t2 Columni Headpiece.
2. False Emp (Buggy, only one real boss to fear Jindo/ship one, requires tactics/interrupts there, and target/CC marking on many groups of mobs... it's long) Drops Chest. Also as said, buggy esp Final Boss.
3. Battle Illum - One boss to fear is Krel- esp for melee, but we got a tactic down and wasn't too hard with it. THo we wiped first attempt. Skip bonus, goes much quicker. Drops t2 offhand.
4. Maelstrom - One of the hardest HM bosses, but get passed him, it's easy. Col Valknar or Eye Implant dude as I call him... expect a few wipes from this guy. Key is for tank to keep aggro on him when his Implant goes off (implant mode = dead in 1-3 hits) so ppl still DPS him in that mode. But he can switch targets easily, if you're melee DPS he'll switch to you first and kill you... This boss is the HM test for all roles, Healer, Tank and DPS).
5. Taral V - Just because we didn't beat it yet but came close... final boss hard. He spawns 4 elite droids 3 times... requires lots of CC and/or kiting boss into another room.
The rest we've not done. So I'd rank Essels next and the hardest Directive 7.