1st – If you attack as you’re coming down from a jump and you’re hitting attack fast enough, you can immediately attack again upon landing. This allows you to hit some enemies far quicker than you normally would be able to. (Mainly larger enemies, but if you’re hitting attack just before landing, you can hit some shorter enemies twice as well).
2nd – You can press attack and back-dash at the same time to do a retreating swing. This is very helpful for those little kobold buggers that like to shank you in the face while you’re still locked into an attack animation otherwise. (Also, exceptionally useful against those dang snakes and their charging at you).
3rd – You can attack “downward” with some weapons (the starting sword, for instance) by aiming a diagonal downward away from you. It’s not a full-on Shovel Knight-style down-stab, mind you, but it can help get an extra hit in on some enemies before they can get in range for damaging you (like the little beetles circling some single character wide platforms).
4th – A quick tip about familiars is that they work much as they do in the 2D Castlevania games; they level up as they damage enemies.
5th – Another non-combat-related tip is to jump around at pretty much any walls you find. Illusionary walls are a thing and sometimes even lead to entirely separate secret areas with a few connected rooms and some extra items and such. (You may not have missed anything major in your playthrough).