I keep lying over small things and i don't know why i keep doing this and want to improve, what can i do?

I know the title seems awful, but here is the deal: i (22 m) sometimes lie to my girlfriend (20m) over small things like the time in which i exited my house to go to hers (not admitting that i am late and putting the blame on something like the traffic) or about the time in which i claned our twister rat's cage (there was this ocasion in which i didn't clean it for 2 days because i was out for a chess tournament and said that all that mess was just from 1 day). The only big lie that i told her was that i wasn't looking to another woman (in an ocasion that i was indeed doing it, because i thought that her hair was nice and her dress was kinda cute). We broke up once (we are back together, but there is still this thing with the lies) due to that because she has some really big traumas related to people lying to her. A big part of those lies were told because she is kinda of an explosive person and i was kinda of afraid of her reactions, but there were some lies that i told her for no specific reason and there were some lies that i told her because i wanted to look nice to her or at least less bad. She notices when i am lying and i really do want to stop, but even though i know the reason, sometimes i do it unconciously. What can i do to improve?

Ps: When we were talking about going back together, one of the things that we adressed were those agressive reactions of hers (she is kinda of a rude person with some anger issues) and she is really putting some work into that, and this made wonders to the relationship and made me be more honest with her.

PS 2: Sorry for the bad english, this is my second language and i wrote this is kinda of a hurry.

PS 3: Thanks in advance for the help