What @qwerm said. Build the Dead Raiser and visit greydwarf spawners in the Black Forest. Let your spawned skeletons pile up greydwarf kills and watch your blood magic level grow. If you park in a small 1x1x1 shack complete with campfire and roof you get a resting bonus while your skeletons do all the work and your leveling is even 50% faster. How much is enough? As much as your patience can stand. Getting to level 50 blood magic requires your skeletons to get just over 5K hits on greydwarves but your protection bubble is extremely strong at that point. Also you can build an elemental magic trainer and likewise grow that skill. My most recent visit to The Queen had a mage with 52 BM and 54 EM and she had no problem coming out with the trophy. I've heard that skills of 75 or more will be needed in the next biome so I'm spending time in this inter-release waiting period to level up.