You can't usually just jump right into it. Most (note the most) of the time, it isn't the cinematic, epic, sudden, perfectly receptive moment. There are quite a few prerequisites to a successful profession of love. You need to make sure she is completely happy, and not wanting for anything more from the moment. The moment should be proceeded by at least a few hours of time together, in which you perform chivalry to the highest degree. You want her attention to be completely focused on you. This is easier in an isolated environment, but can still be accomplished in a public forum if you have the game. You obviously should be looking her in the eye, but you need to convey, (and this takes practice), an energy with your eyes, an intensity so to speak, so she can understand that what is coming isn't just words. And, this is the hardest bit, and the most dispassionate, you need to be sure she already loves you back. If you put her on the spot with this, and she isn't ready for it, you seriously hinder or even cripple the possibility for a future successful profession.
I do not mean to say that this is the only method for going about it. This guideline is from my own and my closest friends' (term used lightly, its just hard not to know everybody's life stories when you go to a boarding schools of less than 300 students for 5 years) experience, it might not apply to everyone. There are contradictions to every rule, and I even have one from my own experience. I myself have dropped the L bomb 3 times in my near 20 years. Perhaps my most intimate relationship (this is saying a lot for an INTP), was with my latest girlfriend (now ex, sadly), and my own rule was completely broken. We met through a mutual friend by accident, over skype of all things. We talked a little bit that night, first jokingly over the camera, then more seriously off. We exchanged numbers, and the conversation never ended, not for the next 11 months. We became fast friends (she is a very smart girl, and I love a good rapport and intellectual stimulation), but did not meet face to face (she went to a different boarding school) for two months. She lived six hours from me, but spent most of her time not at school at a friends house who lives less than an hour away. Over a Christmas break she needed to be picked up from the airport, as she was flying up from a Florida family vacation before her family to spend some time closer to her school friends, but her friend was out of town that night. I offered. Took her to dinner. Went to drop her off at her friends (she had a key). Spent 4 hours parked in the driveway just talking. Kiss happened. Saw her three more times that break before she had to go home. It was amazing. It just felt right. Saying goodbye was terrible.
I couldn't bear the thought of not being able to see her again before going back for another stretch at our separate boarding schools, and having to go back to talking over the phone or on the computer, and I felt regret at not being complete honest and forthcoming about how I felt about her, somewhat out of fear and somewhat out of not being able to find the right words. I was afraid of losing her, and I wanted another chance. So the next morning I woke up extra early, drove 6 hours and arrived at her house unannounced, knocked on the door, got her ginger brother, asked for Emily, she came out, hugged me, looked at me confused, and said what are you doing here. I blanked on my six hour solo drive planned, rehearsed speech about my feelings. So I said I love you. To which she responded with crying. Then kissing me. Which confused and hurt at first until she told me "no it's good tears".
Guess the moral of that ramble is that cinematic sometimes does happen and works too. I also think it might show that I have some unresolved feelings for that girl. I did not plan on sharing/typing all that when I clicked reply. Damn.