Direction. Is the swell inside the spot's window? If it comes from the wrong side the beach will be small or flat, whatever the number says.
Period. Under 8 s is weak, 10 s and over is where most spots start working.
Size at the beach. Look at the surf size, not the swell height, and compare it with what you are happy in.
Wind and its timing. Is it offshore now, and does it turn onshore later? Go early.
Tide. Does the spot need low, mid or high, and when is that?
A camera. If the spot has a free live cam, open it. Nothing beats the real picture.
What the forecast cannot tell you
The grid. Wave models see the sea in squares of about 9 km or more, so near the coast they blur sandbars, headlands and local wind.
Time. Days 1 to 3 are reliable. By day 7 it is a trend. Use the 14-day view to plan, not to decide.
Models disagree. The "Model & buoy checks" section on a spot page shows how far apart they are, and what the nearest buoy is measuring.
At the beach: the 15-minute look
Watch at least two sets. The first one is not the biggest.
Find the rip: a patch where the waves do not break, often darker, with foam or debris moving out. It is the easy way out, and the place to avoid if you are tired.
See where the others take off, and where they paddle back. That is the peak and the channel.
Look for rocks, other surfers, people learning in the whitewater, and your way back in.
If you are not sure, do not go. The sea will be there tomorrow.
The rating in the app (Poor, Fair, Good, Epic) is a simple model of size, period, wind and your level, not a measurement. It is a good way to rank days, and a bad way to overrule your eyes.