there are a lot of things that break tawhid. some of these include:
1) selfishness/selfness
2) pride or arrogance
3) ignorance
4) superstition
5) complaining to ALLAH.......E.G (IF SOMETHING HAPPENS THEN YOU SAY "WHY ME"....THAT BREAKS TAWHID)
6) begging for favours (you will get what you need, when you need it.)
there are a lot more things that break tawhid. to know them all you will have to read the quran and the hadis....
always try your best not to break the tawhid.