The best way is by telling her that she looks nice. Women do a lot of things to get sexy for men and it would be better to let them know just how much they are in your eyes. Compliment her when she does something you like and once in awhile cook for her. You can also do something romantic at least once a month.
next day u have a free day, tell her to jump in the car and take her on a mini vacation. if u don't have much money, bring a picnic basket full of good stuff to enjoy. If u do have money take her to a nice restaurant on your mini vacation. A mini vacation is usually just a day trip but u can take a tent with u and camp out or stay at a cheap hotel for a overnighter. Returning the next day.
Treat her good; treat her nice- but remember: girls like a challenge. If u fawn over her too much, call all the time, she will lose interest. Let her wonder why u aren't calling all the time. Stay back a little. This goes for both boys & girls. Relationships are hard...
Tell her she is beautiful every day and do nice things for her like hold doors open and stuff. Never complain about something that is wrong women hate that if something bugs you talk to her about it. If you have money buy her things if you don't she won't care that much. Lastly women are picky as hell about the way you look try to be understanding of her ridiculous commands.