Mechanical clock not keeping time.

Hey guys, Since joining this forum, I've decided to rewind a cheap mechanical clock that I bought once when I went off on a holiday. In the past, this clock kept pretty decent time. But in recent months, the clock has been losing time every single day - even on a full spring. Short of taking it to a clock/watchmaker, what can I do to get the clock to keep time? I thought a few generous squirts of lubrication-oil would be sufficient to do the job. Is this enough? Or must I do more? Also, what kin