When I read that you really needed 2 weeks to down Grob'thok I think your group lacks a lot of skills. This is not meant to be rude, it's just that this is maybe the easiest Boss I have ever faced in the newer Operations (past KP). It is basically tank&spank and doesn't require hell a lot of tactics.
However, I will try to give my thoughts about what makes a good progression group.
First I have to say, it is essential that you know your advanced class 100%. Make good use of all your abilities and even your skill trees. You need to be able to adapt for bosses. A dps who is always running the "standrad spec" and doesn't know what else he can bring in for a special boss is someone you will not want in your group. Same applies ofc to all other roles.
As mentioned before in this thread, you need one guy in your group that fits the role of a shout-caller. In our group it is always a tank as he has the best overview about the entire raid situation. That guy tells when to use Inspiration, a gunslinger shield, when some special dots are up and on whom (for example Tyrans Infernos), who stays in aoe and has to move out (should be very rare, as all guys should be able to recognize their positioning) etc.
I don't know if I would be up to form a new progression group again. The Team I am in right now is together already for 1 1/2 years (at least the core of 6 people). We know each other very well now so whenever there is new content to clear we take on this challenge with ease. Whenever I join a pug group to clear something on my Alts it feels very frustrating from time to time as you can't rely on these guys. If one guy goes down, a pug group starts panicking and it will result in a wipe.
So my tip is, get to know each other first. Do all kind of stuff together, speak on TS/Mumble so you know the voices of all guys. If someone needs a dispell in a raid group and the healer has to ask "who just said that" is not a good sign.
If you have a good team synergy you will see that doing progression raids is something really entertaining.
In general I mean you need to socialize with your team members. When we're not raiding and hear each other in TS, we are always online in our skype chat group and write about everyday stuff as well as on SWTOR related stuff. That's why I love my raid group and we have good success.