I figured out if you hit an enemy when you start to jump and when you start to fall, then you deal more damage than usual and you also give more knockback.

i'd recommend going into your world settings and changing the simulation distance to 6-10, which can help prevent excessive mob spawning and help with other things as well. this is mentioned in this video: youtube

Sometimes when there are a lot of mobs I'll gather them all up then blow them up with a creeper :)
When fighting a Creeper I also like to crit it once then run away, then charge back and do another crit but then spam instead of running, then it should die, I've only tried it with stone and iron though, and sorry if you get blown up trying to do it lol ._.

Simple tip: avoid any fight you can avoid (Ideally one only sees mobs whenb ankle chopping them for drops. 😇 )
Particularly true before one gets good armor and a shield (and – hopefully – a good weapon[​s]); early game, it's best to avoid mobs and concentrate on getting kitted out.

The biggest thing for any mob type is not to get swarmed: if you got the space run away then fight them one at a time when they string out.
Alternately, one can open up enough space to kill them with a bow avoiding melee entirely (especially useful with creepers).

Above ground, one can pillar up and hit them from above when they can't hit back (doesn't work well for spiders and counterproductive vs skeletons).

Setting a block at player head height, then dropping into a one deep pit and attacking through the opening (preferably also with a slab to stop chuckies) works in a narrow passage (or where one has set up a 'rally point' to which to retreat).

Particularly if one has DepthStrider (which should eb standard equipment outside the nether as soon as practicle), getting into water (or placing a water source) can also give one a significant advantage.

N.B. I don't play br, but all of these involve sufficiently simple mechanics they ought to translate well.