Say it without pressure. Don’t do it because you think you have to; say it because you want to. Don’t say it because someone says it to you. Despite common belief, just because the three words get uttered doesn’t mean that you always have to hear the three words back.
Don’t say it because you want to test out how they feel. If you fall into this trap it becomes an insincere declaration that may result in you biting off more than you can chew.
Only say it when you have all of the relationship basics in place. You don’t say these three words when you’re not even sure whether or not you’re their girlfriend!
Don’t say it in the middle of sex. You may have a captive audience but it could make for a very uncomfortable, if not sex halting moment. Also, if the sex is that great, you may not even know your name anymore, nevermind whether you actually love them or you love the sex!
As it’s the first time, choose your moment well. It’s nice for it to be memorable although you don’t need to have a contrived, slushy moment. It’s best not to say it when they’ve just told you that someone has died.
Don’t say it as a response to being broken up with. Even if you do mean it, the other person is likely to feel pressured and you may come across as desperate. If the person is breaking up with you because they didn’t know how you felt, saying the three words may work, but it could still come across as desperate and insincere.