Tournament Preparation How should someone prepare for a chess tournament? 
Openings? Tactics? Strategy? Endgames?

What are some of the techniques strong players use in order to get ready for an upcoming tournament?

(1800 USCF)
If the opponents are known (e.g. in a round robin tournament) you can prepare specifically for these opponents, i.e. find openings or positions which your opponents don't like or in which they perform badly, etc.Professional players would do this even during the tournament (in-between rounds).

If the opponents are not known (e.g. in a large open tournament) there is not much you can do other than what you should always do: practice tactics, learn/study endgames, strategy, refreshing your openings, doing some sports (not chess)...

Overall at your level I would not worry too much about all this. Arriving relaxed to a match will be more important than trying to prepare specifically for one opponent.