How to practice on EXPLAIN/optimizing queries/constructing indices - Mailing list pgsql-novice

So I found https://wiki.postgresql.org/wiki/Using_EXPLAIN but still I
feel there should be more to it.
What methods can I use to actually get better at spotting issues with a
query? How can I go from looking at a fancy EXPLAIN graph produced by
PgAdmin and realize what the problem is (if there is one)?