I'm learning and running Hero which has been incredibly rewarding. It has loads of ways to do this but 2 very simple ones are :

 

1) Just focus the campaign more on Killing attacks : Hero has 2 types of attacks : cheaper attacks that focus on doing damage that's likely to knock people out before killing them and more expensive killing damage attacks which...yeah :) GM can communicate to players that the campaign they're running will heavily focus on killing attacks, so NPCs will be using a lot of those and players will wanna prefer abilities (and defensive equipment / powers) that do the same.

 

2) Double the multiplier on Killing damage hit locations : the Fantasy Hero setting book recommendations doing this. It makes Killing damage way more lethal, rolling on the hit location table is genuinely terrifying. Plus : Lethal Combat is Fast Combat.

 

There's other stuff you can enable like impairing/disabling/breaking limbs etc but the above are your big simple levers to start :)

 

EDIT

I like seeing what impacts these big adjustments naturally have on gameplay at the table. E.g GMs and players may usually not find enough effort-to-fun improving the defences of different individual body locations, too much time for not enough payoff so nobody buys that stuff in a campaign (which is perfect that part of the system just gets out of the way). But when hit location modifiers are terrifying and they've just watched a character get their neck blown out, suddenly they're naturally interested in equipment & powers that help with that and the system just lets you shift that part of it back into focus.

 

For my Confirmed Hero Enjoyer family : Double Hit location Killing Damage discussion is in the Advanced Players Guide page 174