Spell work is very much trial and error. Don't expect spells to work right off the bat. Give them time, be patient.
Before jumping to conclusions, look at your procedure (what you did during/before/after the spell) and how it can affect the spell. Make sure you followed the spell to almost every detail.
Also, if you are using spells that you have not written, that may be a problem too. If a spell seems foreign to you, you won't connect with it, thus you won't connect with outside forces easily. I suggest you write a spell of your own (which is not that hard and i am sure you can find some tutorials on how to do so), to better align with your energies.