Treat her like you're still trying to win her. You should never stop putting in the effort it took for her to be your girlfriend and just because she is your girl now, that doesn't mean you should text her less, respond to her slower, not make much time for her, not display as much affection, not be as spontaneous, not pay her as much attention, not show her off like you did before, not express your feelings to her like you did before, and not care as much as you did before. The effort that you showed her is what convinced her to give you a chance, to not have any doubts about you, and to believe that you'll remain the same guy through the relationship. It's also that very same effort that is what it's gonna take for you to hold on to her because without it, she has no reassurance that you're right for her and she'll start to think she made a mistake by being with you when she starts getting less and less of it. So don't slack on her, bro, because she wouldn't slack on you.