Graham/Willow became popular during season 4 because of good timing. Their best friends are dating, Willow’s just lost Oz, and Graham, as far as we know, is single. It’s the perfect chance to get these two together. But if that’s what you’re basing your fic on, you run the risk of writing the relationship without any real spark. As easy as it is to pair them, you do need to have your reasons why they would fall for each other as well as some idea of how they should get together.
Although season 4 isn’t the only place to set your fic, it is the easiest to write. Willow hasn’t discovered she’s a lesbian and Graham is in Sunnydale, not off fighting demons who knows where. Past that you have to work around a lot of things, and you need to have a good sense of what is going on at the time to avoid confusing the reader.
Regardless of where you set it, the most important thing to keep in mind through out the fic is interaction. If you’ve watched enough Buffy to understand the characters, you shouldn’t have a problem with characterization. If you’re worried about falling into the stereotyped Willow and Graham, look into each character individually by reading fiction and essays on them. Once you understand each character on their own, you need to think about how they will react to each other. Willow for example is a lot more confident with meeting new people in season 4, and Graham doesn’t seem to have a problem talking to girls (S4 ‘Doomed’). Take each character’s personality traits and opinions and see if they clash anywhere. For example, its unlikely Graham would understand Willow letting Spike live and even working along side him. Willow might not approve of Graham’s work and how little he questions authority. As far as Willow and Graham go, there aren’t any major points they would argue over or dislike about each other, so either working around them or through them will allow you to take the characters into friendship and even further.
One major point to remember is what’s going on for Willow at the time. In season four, she’s either with Oz, devastated about losing Oz or with Tara. Most fic is set after Oz’s departure. If this is the case with yours, don’t simply have Willow forget Oz and get with Graham. She’s in a very bad place after he leaves, and it might take more than a bit of flirting to get her out of it. But you can use that to your advantage. Graham comes across as a really nice guy and a loyal friend. If he can help Willow, be a friend to her, a relationship can come after that. It sounds long winded, but it doesn’t have to be. Just as long as you put across that Willow goes through a rough time, deals with it and moves on, you should be able to make a realistic story. If you set it anywhere else, take note of Willow’s love life. You can pretend Oz/Tara/Kennedy never existed, or set it in between these, but take into consideration Willow’s feelings at these times, and whether she’s up to having a relationship.
Graham’s a very easy character to work with, because there are few rules to stick to. We don’t know anything about his love life or where he is when he’s not in Sunnydale. Therefore, you only need worry about Willow’s life and work around that. The only time that’s bad for Graham is perhaps the end of season 4 when the initiative is in a big mess. He’s very loyal to his job and at that point, Willow is part of the team that is taking his best friend away from him and is partially responsible for everything that is going on. Graham might be too involved in trying to salvage the initiative and stop Adam to even think about relationships. If you want to set a fic at this time, you’d be better sticking with something that incorporates what is going on. For example, an action fic where Willow and Graham are thrown together to work along side each other.
Don’t just limit yourself to the easy options in this pairing. There’s so much possibility and with a good sense of character, an idea for a plot and the right setting, you have the chance to write something no other Willow/Graham writer has ever thought of.