In Path of Exile, there are several ways to gain 10% more maximum life:
Passives:
Life Mastery: Allocating all 6 points in the Life Mastery cluster grants "10% more Maximum Life if you have at least 6 Life Masteries allocated."
Other Life Nodes: Many passive skill trees have nodes that offer increased maximum life, some of which may be specific to certain ascendancy classes.
Gear:
Body Armor: Some body armors have the modifier "Increased Maximum Life." This can range from a small percentage to a significant amount.
Jewels: Certain jewels can have mods like "Increased Maximum Life," "Increased Life per Strength," or "Increased Life per Dexterity."
Other Uniques: Some unique items have life bonuses as part of their base stats or modifiers.
Other Sources:
Bandits: Choosing the bandit reward that gives increased life ("Life" or "Life and Resistances") can provide a flat life bonus.
Pantheon: Certain Pantheon powers can grant increased life or life regeneration, which indirectly contributes to your maximum life.
Calculating your total bonus:
Remember that increased life modifiers are additive, not multiplicative. This means they simply add up directly. For example, if you have 1000 base life and two modifiers that grant 5% increased maximum life each, your final maximum life would be:
1000 (base) + 1000 * 0.05 + 1000 * 0.05 = 1100
Important notes:
There is a hard cap on maximum life at 2,147,483,647 (2^31 – 1).
Some modifiers, like "Increased Life per Strength," require that you have a certain amount of the relevant attribute (Strength in this case) to have any effect.
Choosing the right method:
The best way to gain 10% more maximum life depends on your build, playstyle, and budget. If you’re on a tight budget, allocating points in the Life Mastery cluster and choosing the right bandit reward are good options. If you have more currency, you can invest in gear with life modifiers or jewels with specific life stats.
I hope this information helps! If you have any further questions or need specific recommendations based on your build, feel free to ask.