If you can connect with the audience and it makes them feel the feel the songs purpose (sad,happy,loved up). If it has true feelings and emotions (better if from personal experience). If your not sure about a song,record it, close your eyes and listen too it. if it's sounds good then it's most likely a good song. Ignore the singing if your a bad singer though Use a thesaurus. instead of forcing a rhyme look up another word for it, if there's none rewrite the two rhyming lines. You never know,you could think of something better. try and spend 30mins a night writing. It will improve a lot. WARNING: I'm no expert I'm just a 12 year old girl who lives in the countryside so I'm no expert. But I do  writing songs and singing too. I use writing songs too help me get through hard times. I would rather write than talk. But I think I'm not sure if I'm a good singer so if anyone has any techniques to find out ? Iv heard singing against a wall and putting your fingers in your ears so you can't hear anything else apart from singing but that's it. I CAN NOT get a singing teacher.