Pick up a sword, belt up a suit of armor, and start dealing some damage.
Even outside of the role playing elements there is some very important long term planning in playing a fighter.
Plan poorly and suddenly the monster encounters will quickly put you down and put the party at risk- especially with everybody counting on you to deal out consistent damage.
So what’s the plan?
At the lower levels of the game (1-5) armor is very important. With some heavy armor, a shield, and perhaps a +1 magic item for you armor class it will be enough to deflect damage and prevent monsters from hitting you.
Most of your coin and resources should go into armor.
Second to this is adding a +1 magic weapon- sword, axe, whatever your build is playing for increased damage and a +1 chance to hit.
Potion wise you want to obtain a few healing potions, since you will be taking damage each turn by being at the front, and the cleric might not always be around.
At mid levels (5-8) armor class is still important, but it starts to be less effective. More and more monster encounters will be able to bypass it, or hit you with non AC related attacks- gazes, paralysis, etc.
Upgrading your magic weapon with a secondary effect such as ice, shock, flame, also begins to become important.
Depending on the campaign you are playing in and your cash flow you want to buy or start saving for a secondary way of moving- boots of speed, fly, levitation, etc. to help you get around the battlefield quicker.
At levels 10+ armor becomes less and less important- that red dragon is going to star with a +15 to hit modifier even BEFORE the dungeon master roll the D20. Shift your armor over to damage reduction even if it is only DR 2 or DR 5- every bit will help.
Along the way at all levels you are going to want to work on boosting your strength and constitution so you hit harder and longer.
Who said playing a fighter required no planning and was easy?