Survive first. You are of no use to someone if you constatly die and can't help kill. Go weapons, then shield/armor/dropsuit. The militia Logi tools work well enough to be effective until you can afford to skill them up.

For me, I invested in armor repair so that I can heal myself as a medic.

This does absolutely no good for infantry besides unlocking armor repairers. The repair from infantry armor repairers is too small to get a bonus from this skill.

Vehicles get enough armor repair for this bonus to be meaningful.

Help

I upped my shield skills to be able to get an advanced shield.
Best as I can tell, the better shields provide less additional HP than what equates to a single bullet from a militia AR; going that route doesn't seem to improve survivability beyond taking a single hit more (at best).

So how to actually improve HPs to a point where I can take 2-4 more hits, or have a bit more time to run away (better part of valor)?

Okay, based on the thread I am going to assume you're running logi.

So first thing: Don't run away. As a logi, especially lower level, it is almost always a death sentence. You are too slow and your hit-box is too large. Instead, strafe, move back and forth unpredictably, look for cover, and shoot back to disrupt their aim (Mass Driver is great for this). You'll win a surprising amount of those firefights if you stay near cover and on the move when attacked. Higher ground never hurts either.

Second: NEVER be alone. I know this isn't possible all the time, but as a logi, you are support. PvP combat is not what you are built for. Being Rambo in a Logi suit makes no sense at all. You'll die a lot less if the enemy has 2 or more targets to pay attention to. If you don't have friends or a corp you play with, annonce yourself as a logi looking for squad in your local chat. People will group up with you.

Third: When it comes to the dropsuit, you are right, one advanced shield module isn't a ton more HP. Definitely not enough to hold off a good attacker. So, double them up. 2 is better than one, that will get you strong enough to react to an unseen attack instead of just dropping dead. I can't remember off the top of my head if a militia or basic logiu suit has 1 or 2 high slots, but if it is only 1, spec into the next level dropsuit ASAP. Also, if in need of more PG or CPU there are milita modules as well. Drop the cardiac regulator if you have to, it is next to useless for a logi anyway (see: Don't run away).

Fourth: Make sure you have a weapon that can kill. Spec up weaponry for damage boost and get a better weapon, whatever you choose to use. (Merc pack Sub-machine gun and Shotgun are great to start with)

Finally: Be prepared to die, A LOT. Especially with logi, it is a grind to get yourself in a position to survive attacks alone, but once you do you become a beast on the battlefield, able to organize, repair, resurrect, and refill your fellow soldiers as well as wreck any enemy that tries to stop you. My favorite class and worth every moment of the grind.

Hope I helped, feel free to contact me more or check out my corp for further assistance. In-game mail works great if not on this forum

Sake Monster, Tritan Industries

P.S. Upping dropsuit command is usually underrated. Having a lower signature profile means you are hunted less and catch enemies off guard more, a HUGE advantage, especially as a logi.

Survive first. You are of no use to someone if you constatly die and can't help kill. Go weapons, then shield/armor/dropsuit. The militia Logi tools work well enough to be effective until you can afford to skill them up.