What you need to start off.

Well first you need a solid starting point. You need all the basic items.
Food-
You will need crates of capped food which depending on the profession might differ from others.
Armor- (all except trader, and jedi need)
No matter what profession you are nowadays primus capped battle armor is best for any job. I suggest a good 6600 kin/eng 5400 elements. After that you need to mod up the suit with triple 35's per piece. The mods all depend on your build so check out helpful builds I will be posting to better help decide.
Basic Buffs-
Get a familiar! Depending on your build again you need to try getting a familiar for there bonus. Gackle Bats give you 40 pre and 40 str, Mynocks give you 40 agi, Mouse Driods give you 40 con. The musty injector is extremely effective and easy to get. You already have a musty injector, but if you don't make it a priority! It gives a +100 pre +100 str and has duration of 30 min, but you can reapply it every 2-5 mins I forget.
Advanced Buffs-
Then go into more advanced buffs such as Shard of the Serpent for needed elemental protection. You will need this in instances like Exar Kun and in PvP against commandos. (not needed, but would make a huge difference if you had it) The Sith Holocron is useful to have it gives 150 con/stam for 3 min with a 60 min CD (cooldown timer) You should be getting the lair crystal/shard of retaliation. I suggest doing the quest and getting the lair crystal since it's no trade then later buying a shard of retaliation so you can have both. Revitalization Pack which is looted is an awesome buff that gives +200 con/luck/agi for 3 min and CD is 30 min.
Misc Items You Should Get-
I think A Sprint Enhancement Stim is always great help no matter what prof you are. It gives a boost like a jedi's force run for 60 sec and you can use it every 30 min.
Get an Officer-
I say this makes a Huge difference when either PvPing or PvEing. If you have the chance make an officer alt same server and lvl him up to 90 just to drop stim when you need. If you can't do that then make friends with officers that are always on and see if they are willing to drop for you. The Tacts Stims in my opinion are the best buff ingame that you can have pretty much all the time. Then the Med Stims are a a big help especially if your one of those professions that as a low heal. Now even though it doesn't define the player by making or breaking it, but it sure does add a nice advantage over most other players.
Medic Buffs-
For this you should have access to a AFK medic buffer with 1 hr 30 min buffs. Most servers have AFK medic buffers for all to use which is great. You should always tip those medic that do because they are providing a public service that everyone uses. If your server doesn't however then you should join a guild that has a buffhouse near restuss. (provided your not in a guild already)
Entertainer Buff-
Always get an entertainer buff no matter what you do. They are extemely helpful. Now there isn't any universal buff to help with any profession so on this you will need to customize it to maximize your build.