I'm a Gallente tanker, and I'll share some info with you. Keep in mind, there are a hundred different people who will give you a hundred different fits, and this is what has worked for me.
First of all, before you even put points into Gallente HAV, get your modules and core skills up first. The Soma militia tank will do you just fine to start with, but if you already skilled into Gallente HAV then go ahead and proceed. I'll assume you have already jumped into the Gallente Madrugar for the sake of my little sermon.
Since you went Gallente, you will want to exploit its natural armor tank ability. So skill into armor before you do anything else. This will give you some survivability and will keep you from losing tanks left and right. I got armor adaptation up to LV 5 before anything else (ok get LV 1 armor repair first so you can equip a repper), which allowed me to stack active armor hardeners which give you a 25% resistance each. Next up is armor plating. Though you only need to get to LV 3 to use all the armor plates available, trust me you want to get this up to LV 5 for the PG reduction. Armor plates, especially the 180mm's, are PG HOGS and you are going to want to save as much PG as you can. You will benefit from skilling into armor reppers and fitting the best repper your PG will allow. This is very important and i'd advise to get the best repper you can fit asap.
Along with skilling your armor up, make sure you are also putting SP into your core skills...electronics and engineering. ESPECIALLY engineering, because this will let you use the PG modules, which increase your total PG, and trust me, you're going to need AT LEAST one in your fit.
A module I stand by 100% (and I'm sure alot of blaster tankers out there will agree), is ACTIVE HEAT SINKS. You only need LV 3 in turret upgrades to get you the best active heat sink, which reduces your heat build up by 52%. In other words, you can fire twice as many rounds before you overheat. This is normally the difference between life and death when you're in a tank vs tank battle.
Notice I haven't even touched weapon skills or turrets yet. You want survivability over damage when starting out. Once you put together some decent fits that allow you to stay alive longer, then and only then should you start thinking about turret operations.
Anyway...that's my rant. I have multiple different fits for different battle situations. For example, if the enemy is spamming tanks, I have a fit that i strictly use for anti tank purposes. it's comprised of an active and passive heat sink so I can dish out as many rounds as possible. When the other tank overheats i'm blasting away. I also have fitted the best repper i can fit, a hardener, a damage control unit, (which i rotate so i always have an armor buff), 180mm polys, and a pg module.
Other fits are more for anti infantry that are spamming AV weapons where I swap the passive heat sink for another hardener
I am always theory-crafting fits for my tanks to fit different situations, and you will too. Just make sure to save as much PG and CPU as you can by equipping PG modules, and skilling into your core skills.
This is in no way the definitive guide to tanking. Check out void echo's guide to tanking...he's an awesome guy, one of the elite tankers in Dust, and has no problems walking you through some (and i mean SOME) of his fitting advice. There are some other good HAV guides to check out as well.
https://forums.dust514.com/default.aspx?g=posts&m=932572#post932572