One peculiar thing about the skill upgrades in Shadow of War is that only one upgrade can be active at a time. The key thing to remember is that this choice can be switched whenever you like, even in combat. Maximize Talion's effectiveness by always having the right profile active. One of the most common switches, for example, is going to be around the Treasure Hunter skill. Anytime you see a gem-carrier, you'll want to switch it to Prospector, to get the best gems. Anytime you go up against a captain, warchief, or fortress, you'll want it set to Discerning Eye, to score the best loot. And even then, you might take out a captain, switch when you notice a gem-carrier in the crowd, then switch back after you've killed him, and are now hunting down assault leader number two.
Switching from Dominate to Quiver of Souls is another common one, depending on your elf shot needs, and again you might switch it back and forth several times during a fight.
To a lesser extent, the same is true of gems and gear. In a tight spot, you might switch out the XP enhancing Wealth gems on your armor for Life instead, or swap your highest potence gem from bow to sword when you come across an Arrowproof captain. And while you aren't going to acquire the same breadth of weapons as a Diablo character, you might still want to switch between poison inducing weapons, fire inducing weapons, and head exploding weapons as circumstances dictate. Likewise, items that empower followers can be useless during missions but vital during a siege.
Switching around your gear and specialties like this is a free action, and while it may be fiddly, it's better to spend an extra twenty seconds on optimization than an extra twenty minutes gathering more gems, or recovering from a sudden (and totally unexpected) relapse of death.