play engi, he will show you what spy can really do, then equip stock, i know the kunai looks good, but its a sham, then use the diamond back(yes i know its a "sweat weapon" but if you need to pull out your gun its good to have crits), use maps like TF2_Walk to help with aim, then play some casual, watch some tutorials, and remember, you are the spy, you may be squishy, and you may not be a great damager, but with paitience, positioning, and some gamesense, you can turn a server into an absolute clusterf**k of the enemy team worrying about you and you killing them.
-A Spy main with 2000+ hours on the class
(for more tips pleae follow me, i would love to help)