These things help make the vampire break in more likely to happen:
1. You have to have your sim(s) talk about vampires a couple of times to toggle vampires to more active in your games (talk about/make alien joke seems to help with getting aliens to activate in your game (not trigger abduction but be more active as townies).
2. Vlad will contact you about how lovely your neck is and once this happens, in one to three games nights he will appear on your sim's doorstep.
3. All of your sims must be in bed asleep before 10:20 p.m. when Vlad drops by or the break-in won't happen.
Good luck to everyone wanting their sim to become Vlad's late night snack. ;)
Side note: MCCC has a risky vampire setting that will allow your sim a percentage chance, that you choose, of being turned when bitten and the percentage chance of being bitten by a vampire.