Although I concur to a degree that “your weapon is an extension of your arm”, I feel this ignores the personality of your chosen weapon. I need hardly mention that a head-heavy mace will kill in a very different manner to a sharp lightweight sword. Always fight in a way that brings out the weapon’s greatest advantages, for example deliberately using a cross-guard not just to parry but trap and bind a foe’s weapon before sliding along with a safe thrust.
Any half-decent fighter shouldn’t consider just techniques but also surrounding circumstances. Being on higher ground, taking your opponent by surprise, training to be stronger and faster, even something as simple as keeping the sun behind your back can stack the cards in your favour. Never assume you will win and always be prepared for your opponent trying something crafty.
Range is always a significant advantage, so hence a moderately trained spearman has an advantage against a moderately trained swordsman, and a decisive advantage against an equally trained knifeman. Sometimes hecklers on the internet say “what about guns” and other such filler but the truth is that throughout history close combatants have been painfully aware of projectile weapons and how they give an even greater reach advantage than the longest pike. Think about how you can take an opponent’s reach advantage away, just like in my first point.
Train and practice against different opponents and ideally against different styles as well. If for example we asked age-old questions like “who would win, Knight or Samurai”, then any gambler should put his or her money on the individual who understands the other better. Going into combat against someone whose style you are not used to fighting against is incredibly dangerous, so the more you train and safely spar against different schools of combat, the better your chances against a new foe.
Although it’s sad to admit it sometimes, fitness plays a strong role is all forms of combat, indeed we even see lightweight and recoil compensated firearms being best wielded by strong and agile soldiers. Close combat with weapons requires not just raw strength but plenty of speed and endurance, so make sure to train your body generally to be useful but also train in the most strenuous actions you will perform, such as holding a high guard. Unarmed combat is noticeably the most fitness-determined type of combat and usually winning fighters need similar or superior fitness across the board.