So I made this quick guide for the benefit of other players who want to become vampires. A lot of the guides I saw online glossed over certain points which made the process more confusing than it needs to be. So I hope to clear some of those up here.
This guide is assuming that you want to become a vampire the "normal" way...that is not giving absurd amounts of cash to other PC vampires hoping they won't rip you off, or spending years in a guild having to "prove" yourself first, or begging PC Vampires for free bites. This guide centers on the Daggerfall Covenant...if you are in another alliance, sorry. But a lot of this info probably applies to you anyway. So it is worth reading. I won't go over stuff I know is found in other guides.
1) People keep saying you need to find bloodfiends in the middle of the night. Wrong. I got bit right before sunrise, when the sky was light, and birds were chirping. So do not give up just because the sky got lighter. This map shows the location of where the spawn was that bit me.
You need to get bit by Bloodfiends to start the process...they typically spawn in pairs. You may need to get bit more than once (getting killed is fine and may even be preferrable)...I got killed twice before I saw I was infected.
2) The signs of infection are NOT obvious. People said you would see a message or something...I never saw any message. The only way I knew I was infected was by seeing a message in my slotting screen...at the bottom it said under "active effects" that I was infected by vampirism. Until you see this you should assume you are not infected, and keep trying.
3) After infection, you will need to talk to an NPC to obtain the quest. This NPC will appear as a vampire standing by a wayshrine (any wayshrine...and I assume he will continue appearing until you talk to him). He looks like this:
4) He is where you get the "Scion of the Blood Matron" quest. You dialog with him and he directs you to another NPC, Rahaja. You will find her on the map (in my case her location was right next to where I got bit). She is inside a doorway which itself is an an alcove in the rock. She will explain the process of what you're expected to do. It involved drinking from some special basins (giant bowls) and experiencing a recreation of when Mother Lamae was first turned.
5) After experiencing both basins you talk to Mother Lamae, and they do a rtiual that drains you. You are a vampire at this point, technically. You can feed but won't have access to the vampire skill line yet.
6) Another door at the back of the room leads to tunnels. In the tunnels are human assassins called "Worms". They are level 41 and 42. You need to kill 10 of them. You are expected to feed on them, but this is not required. All that is required to complete the quest is to kill them. And yes, they do respawn. As a level 33 Sorcerer, I did not have a huge problem soloing them although they did resist my spells a lot. So if you are a caster, be prepared for that. I had heard you could kite them, but the tunnels do not leave a lot of room for kiting IMO. I did not see a way to get back to mother Lamae (there is a cliff you drop off of to get to them, and you cannot scale back up it). I just killed myself and respawned back in the first room. This will happen whenever you die fighting the assassins.
7) Once this is complete, you return to Mother Lamae to complete the quest, and are officially a Vampire after that. You now have access to the vampire skill line.