Two players of equal quality can be worth completely different amounts depending on who they play next. Fixtures are the single most useful planning tool in FPL, and learning to read them properly is what separates organised managers from reactive ones.
Short-term vs long-term fixtures
Short-term fixtures - the next two or three matches - decide your immediate transfers and captain. Long-term fixtures - the next six to eight matches - decide your Wildcard and your squad structure. A player with one great fixture followed by five brutal ones is a one-week rental, not a signing. A player with an average next match but a kind run after it is a patient buy.
Home and away matters more than you think
Most teams attack better and concede less at home. A mid-table side at home against a struggling defence can be a better attacking pick than a top side away at a rival. When you compare two similar players, the home fixture usually breaks the tie.
Fixture swings and doubles
Watch for swings: a team whose fixtures turn kind for a long stretch is a buying opportunity, and a team whose fixtures turn nasty is a selling signal even if their form looks fine. Later in the season, postponed matches create double gameweeks, when a team plays twice in one week - those weeks are where chips and careful planning pay off most.
Do not over-read a single fixture
One kind fixture does not make a bad player good, and one hard fixture does not make a great player bad. Use fixtures to choose between close options and to time your moves, not to rebuild your team every week. The best fixture plan is the one you can actually stick to.