In short: epic arc cycling. Each faction has its own plus Sisters of EvE arc where you can choose the faction at the end. Those arcs give a high faction standing boost as reward without a penalty to the opposing faction.
As you can repeat the arcs every 3 month, it will probably take more than a year from scratch. You also need to farm the standings for arc access first, and train the ship skills to run them. It can be a long term goal.
Whether you need it, is another question. There is little use of overall high faction standing, except with Caldari (Jita fees). I personally have +5 with all four, because I want to be able to use lvl4 locator agents across empire space.
EDIT: Context, having high faction standing with all factions is not foreseen by the game, the regular plot is that you decide for either side Caldari/Amarr or Gallente/Minmatar. That there is a way is expression of emergent gameplay which was accepted by CCP, otherwise they would have patched it out, but they certainly don’t support it.