You have to pay attention to the protagonist's stamina at all times. This element works similarly to, for example, that from the Dark Souls series. The Stamina bar diminishes every time you perform an action that takes physical effort - these include attacking with melee weapons and running, among other things. You have to avoid depleting the bar completely because the protagonist will then become severely weakened and thus vulnerable to enemy attacks. Try to launch singular and accurate melee attacks instead of swinging your weapon blindly. As for sprinting, use it only when you have to quickly withdraw in combat or displace to avoid taking damage.
Stamina is not the only factor you should pay attention to. Health and Suit Integrity are also important. Health points can be replenished the easiest by using medkits that you can find in the game world. If you need to regain only several points and you're not in a hurry (meaning not under attack), it's best to use food and drink. Unfortunately, such consumable items restore only a few Health points. In some places, you can also find medical operators which are flying drones. You can approach such an operator and "demand" that it heals you.
Suit Repair Kits are best for replenishing Suit Integrity points. Such kits restore 25 points by default. They can be found in the game world quite often but do try to use them only when you can utilize them to the fullest (when the suit is damaged more seriously).
You can take care of Health and Stamina better by unlocking certain abilities. Doing so is especially advisable at higher difficulty levels. Consider unlocking the following human abilities:
- Physician I and Physician II - you can increase the medkit effectiveness up to 300 percent.
- Metabolic Boost - elongates the duration of the Well Fed bonus (statuses are described in the farther part of the guide).
- Conditioning - permanent boosts to Health (+15 points) and Stamina (+5 points).
- Toughness I-III - you can enlarge the Health bar up to 300 points.
- Stamina I and Stamina II - you can permanently enlarge the Stamina bar up to 150 points.