I have two "rules" I tend to follow when I do include romance in my stories.
The first is the Doug and Carol rule. Doug and Carol are my favorite couple from ER, my favorite show, and even though they were clearly meant to be, they didn't get together until Season 4. When they finally did, it made their relationship that much better, because it had taken so much time and so much drama for it to happen. The lesson I took away from that was to draw it out (without making it too boring or infuriating), to make it more gratifying in the end.
The other is the Jack and Rose rule. I remember taking a trivia quiz on Titanic in a magazine, shortly after it came out, and one of the questions was, "How many times do Jack and Rose say 'I love you' to each other?" I think the choices were 0, 1, or 2; I just know I picked 2, obviously, because they were so in love, it had to be the maximum number of times, right? I was surprised to find the answer was only 1; Rose says it once, when they're in the water and she's saying her goodbyes. Jack never says it at all. That fact makes the one time it does get said that much more meaningful. The lesson I took away from that was to use the L-word sparingly, to make it count more when it does finally get used.
It's tempting to rush it, but more satisfying if you don't.