Here are some things that are not likely to help performance. They stem from out-of-date information and/or naivety.
PARTITIONingrarely provides performance benefits; it can even hurt performance.
query_cache_sizebigger than 100M will usually hurt performance.
my.cnfmay lead to 'swapping', which is a serious performance problem.
INDEX(foo(20))) are generally useless.
OPTIMIZE TABLEis almost always useless. (And it involves locking the table.)