Tips
Make a cohesive story overall, VtM works best when treated as a mini-series with a planned end and every session working towards that end
Always keep in mind the rules of the camarilla, in my experience players are most likely to forget to keep the masquerade (stay subtle so people dont learn vampires exist
Try to remember the difference between clans, ventrue are rich assholes, toreador are the type to go to the fyre festival, tremere are academics, etc.
Enforce rouse checks, making players hunt to drink blood is a core part of the experience. Without drinking blood kindred are just stronger people with powers.
A good thing to do is keep track of the date, hours are less important but it adds to the experience if weeks and months actually have meaning
Dont add too many hats onto the game, if you already have 2 main antagonists you dont really need a third. Theres plenty you can do to make those 2 more intimidating, killing NPC's, having them diablerize a more powerful vampire, having them attack the PC's in new ways, etc.
Tips on starting the game
The hardest part when I created my game was making the first few adventures. Players typically havent fully created their character by the first session, their backstories might be done along with the stats, but they havent grasped the personality. Once theyve fully figured that out its easier to think of new problems that could be interesting for them to solve. One of the more interesting opening adventures imo is to have them solve a small mystery and explore the setting. This can introduce them to more NPC's, introduce them to kindred society, and has the potential to lead into a far bigger mystery. Below are a few setups to the smaller mystery.
A human has been killed and fed on without the bites being covered up, breaking the masquerade
A local kindred has gone missing, the camarilla or the anarchs are prime suspects
A local kindred has sired a new progeny without permission, you must find both of them and bring them to the camarilla (or not if it goes against the characters morals)