I forgot about the guide, its somewhere at games faq. But basically the idea for all of them is the same.

For WT
Every stage, kill as little bosses as possible. Just make sure you get access to the BP NPC and Primeval Demon is enough. Then go suicide in body till WT is pure black, find the BP NPC and own him, DO NOT GO BACK TO TOWN! Find the Primeval Demon and kill it, THEN you can go back to town if you want. Pure black WT is -6, killing a BP NPC gives you +3, and killing the Primeval Demon gives you +2, so you are +5 now, kill 1 more boss and you're pure white WT. With this trick alone you can get to pure black WT and back to pure white WT easily. If you want to die to get rid of body form please suicide at the Nexus and not at any of the worlds.

For CT
You start at 0 CT which is neutral. Killing each BP NPC gives you +1, so after killing 5 you are at pure white CT. After attaining pure white CT, you can start pure black CT by killing the vendors on each world, you know, those vendors who sells you stuff, each world has 1. Killing each gives you -2 CT, so after killing 5, you get to -5 which is pure black, then you can start doing your Mephistophel quest. Suggest you start it before killing Allant.

As you can see, your second playthrough will be the toughest because you will be at pure black CT AND pure black WT and start grinding back to neutral CT by the end of game 2, so make sure you have enough firepower ^^ Grind as much as you can using the stormruler as you can oneshot those mantras at your first game, if you do it nicely you can finish all of them with 3-4 swings then repeat. Once you hit the second game you can no longer 1 shot them making this grind method useless.