A guide to a successful romancing?

I'm sure they've tweaked it a bit. I'm having a harder time too. I still do all the same things though if they are easy prey. I put out romantic aura stuff if handy and just go for it. Flirt, ask if single, compliment... Don't confess attraction too soon and don't use the normal pick up line... If your sim gets confident use the bold pick up line for sure. Then I have them sit with my sim and use most of the other interactions that are available then. If they get a rejection I usually go back to non flirty interacions to bring up the friendship a bit then send them home to flirt another day. If your sim is tense, uncomfortable or embarrassed they seem to fail easier.
I don't even bother now with unflirty sims.. way to hard. Married sims can be harder depending on traits. If they are uncomfortable make them comfortable, happy ect.. It can work sometimes but it's pretty likely to go wrong.