your lucky to have a disposition that is receptive to the dharma, this alone is cause for gratitude in your life, and not bitterness. metta is like the sun, it is warm and shiney and includes ALL beings in its dispensation of comfort. metta will cause pleasant dreams, make your face radiant, stop nightmares, make you fall asleep easy, wake easy, people gods, and animals will love you. start practicing metta by direction good wishes towards yourself love yourself just as you are and mentally repeat these phrases. may i be free from danger, then pause a little while waiting for the emotional response to occur, then say may i be happy, may i be healthy, may i live with ease. between each line wait until the emotion kicks up before going to the next line. then think of a good friend, and repeat the phrases, pausing in between. then a neutral person meaning someone you have no liking or disliking towards. i wouldnt recommend doing metta with an enemy in the beginning because you are likely to cultivate hate towards them. in my experience its best to bring up the enemy after youve got a lot of momentum with the metta, and then loving the enemy becomes possible. good luck on your spiritual journey, rememeber how fortunate you are to have been born a human, to have been born with the buddhas teachings present, and to have an affinity towards the teachings, this should make you very happy and grateful.
take care of mindfulness, and mindfulness will take care of you.