Radiation and poison
Getting poisoned is a very rare occurence in the game and it can happen if you're attacked by a radscorpion. I've already said that radscorpions are relatively hard to kill, so the best outcome is to outrun them, especially if you don't have powerful weapons or explosives in your possession. The best way to protect yourself against the effects of a poisoning is to increase your endurance. This will allow your organism to "swallow" a lot of poison, limiting your health losses.
You definitely have more choices when it comes to fighting off the radiation and protecting yourself against it. Thankfully the radiation is not as nasty as in "S.T.A.L.K.E.R." series, because you will be allowed to continue your journey even when you've been exposed to large doses. The best solution here is to wear antiradiation suits each time you plan on visiting an irradiated area or when you want to swim somewhere. This can only work when you expect to encounter radiation. Otherwise you will have to rely on other means of protecting yourself. A good solution is to use Rad-X and AntiRad medical drugs. The first one can make your organism more immune to the effects of the radiation. As for RadAway, it can lower the amount of radiation you've already received. You can also seek out help at local doctors, but sadly you must pay a lot of bottle caps for their services. As a result I would recommend not selling radiation drugs, because you never know when you might need them.
In order to find out how much radiation you've already received you must open your Pip-Boy. 1000 rads is a lethal dosage, however receiving less radiation can also have bad side effects. For example, your endurance, agility and strength may be lowered significantly and this will only make your progress more difficult. During the exploration of Capitol Wasteland avoid highly radiated areas. Each time you'll be presented with an information on how many rads you're receiving per second. 10 rads and below is acceptable, however you must still monitor your health, so you won't die by mistake.
The game has a relatively primitive module responsible for the simulation of body injuries. Each of your four limbs (plus the head) has its own health bar and it tells you whether you have to use medical supplies or not. If you're dealing with a serious injury you might want to stop your journey for a while to treat your wounds. The most obvious solution is to use medical supplies. In order to do that you must use a stimpak directly on the Pip-Boy screen by clicking on an injured wound. You can also head over to one of the doctors or try to sleep it off (using your own bed in Megaton/Tenpenny Tower or a rented one). I wouldn't recommend ignoring serious injuries, because you'll be dealing with serious side effects. For example, the screen may get all blurry or you may find out that you can't run.
You can use the body injuries mechanism against your foes, especially when you're dealing with fast creatures like deathclaws. Injuring their limbs can result in making them slower or leaving them without guns. Experiment with shooting at different limbs and you'll soon notice all the advantages of precise aiming.
A much smaller risk presents itself each time you eat food or drink unrefined water. I guess I should remind you that you won't need to eat nor drink to survive and you can also rely solely on the stimpaks you find in the wasteland or purchase from the merchants. If you decide to rely also on food, you should focus your efforts on acquiring a food sanitizer from Moira. You can also consider choosing a Lead belly perk. The results will be significant, because you'll receive 50% less radiation.