Concentration is one of BG3's most important spellcasting constraints. A character can normally maintain only one concentration spell at a time, so spell choices compete with each other even when you have enough spell slots.
Do not overfill the spell list
If several favorite spells all require concentration, they cannot all be active together on the same character. Keep non-concentration alternatives available.
Protect the caster
Positioning, armor choices, defensive spells and Constitution support can all help keep an important concentration effect active longer.
Party coordination
Spread concentration responsibilities across multiple characters when the party needs several persistent effects. One caster does not have to maintain every buff or control spell.
Choose concentration by encounter
Use the effect that solves the current problem: control, defense, damage support or utility. Do not default to the same spell when another one would change the fight more.
Concentration and build planning
When a build depends heavily on one concentration spell, treat keeping that spell active as part of the build's core loop.