Using a wider variety of words prevents your posts from becoming too stale, as repeated use of the same thing can be both irritating to the ear and numbing to the brain. Imagine someone trying to explain something to you using the same word over and over: "That thing isn't like that thing; it's more like that thing." This is a drastic example but it is the most blunt way to get the point across.

The common way to freshen up a sentence is to use homonyms; homonym is just a fancy way of saying words that mean the same thing. For example, in a Bleach Role Play like this one, a common word that would be used is sword. Instead of saying sword all the time, there are many homonyms that can be used in it's place, such as blade, Zanpakutou, Soul Cutter, weapon, or even describing it's class of weapon, such as katana, claymore, or cutlass.

Another means of avoiding reused words is by description. If you feel you are saying sword too much, you can instead go into detail about what the weapon is like. EX: "Granleon took his sword in hand. Gazing down at the silver bladed instrument of war, he tightened it's grip on the handle." There, I was able to avoid repeating the word, as well as increasing my sentence four words by replacing "sword" with "silver bladed instrument of war"

Online resources, such as thesaurus.com, can provide you with alternate wordings, so if you become stuck for a homonym, you can go there and type in the word you wish to replace. Making use of such sites as these can build your vocabulary, as well as word of the day sites that provide you additions to your everyday usage of the written language.