On being a good Seme
Dry reference material: http://en.wikipedia.org/wiki/Yaoi#Seme_and_uke
This is character roleplay, you need to get inside the head of your Seme.
Source for image on the right: http://www.pixiv.net/member_illust.php?mode=medium&illust_id=8524045
The closest western description is probably a "power-exchange relationship". This is misleading because power-exchange carries too many sexual connotations.
A yaoi relationship instead revolves around each partner being heavily reliant on each other for emotional fulfilment.
Social factors create tension, and it is up to the lovers to resolve it. Each character's actions are driven by their differing personalities, and it's these behaviours that "make" the Seme or Uke roles.
Your seme tends to be:
In contrast, the uke is kinda boring :P
- Unsure and/or insecure
- Honest with themselves about their feelings
They're both hopeless communicators though - there's your first chapter worth of drama right there. Then they can misunderstand each other's behaviour a bit later on; that's another chapter or two of drama to resolve.
Both characters want to express their love for their partner. At all times. This will create tension and misunderstandings because they don't "get" each other.
Your seme is generally assertive and firm-minded in their actions, but that doesn't rule out variations in personalities and expression. The examples here tend towards an aggressive, but composed seme, without being sadistic.
- You desire to physically dominate - no real explanation, it's just how you roll, it's what turns you on. You may be agressive in... showing your affection, stealing kisses, physical restraint
- Constant attention, maybe a bit overbearing - works well if your uke is of the more "helpless" type
Domination may be mental as well - effected through your demeanour, speech, body language, implied (sexy) threats, etc. As the seme, you want to be in their heart and mind all the time, the centre of their attention. The threats are the manifestation of your possessive and jealous tendencies - it wouldn't do to have your lover snatched away by someone else now. Got a good raep face? Now's a good time for it. Anything like this is fine too.
A "darker" or more assertive seme cares not for social mores - within limits. Is it a problem that I'm kissing you in public? It's okay, this train carriage is mostly empty... I'll show everyone that you belong to me! Pride, jealousy, confidence, a little recklessness - it's all right here, at once.
えー a seme might be a little impulsive too; you didn't warn them about that last bullet-point. Oh, but you enjoyed it, didn't you..? （ドキドキ） Your heart froze, but just for just a moment. Because you knew it'd be okay because it's me.