The idea of using a bath to assist you stems from the fact that heat and cold directly affects our skin pores. We breath with more than our lungs and mouths. This is a way to tap into this. I will not lay out specifics such as which herbs or moon phases to use as it defeats the purpose of having a personalized spell or ritual. The more you put into something the more you'll receive. The other main reason is due to the simple fact that I can't interpret your intentions and some ingredients do not mix well with certain intentions.
Before you enter the bathroom, place yourself into a state of mental equilibrium and center yourself with the universe. Give yourself time to go through your intentions, desires, and actions. Set a timer for more than twenty minutes and get yourself feeling comfy cozy but focused and aware of your mission.
When you enter the bathroom, make sure the bath has been thoroughly cleaned. You do not want someone's groggy morning shower mojo mixing with your trance mojo you're trying to build up. Use bleach or crystals, at your discretion.
Fill the tub with lukewarm water to ankle level. Now is the time to add your ingredients. Once again, the ingredients you use are up to your and your budget's discretion. Once added, stir in a clock wise motion with your dominant hand. Visualize the items spreading through the water on the deepest level and the energy of those items beginning to mix with the water. Once again, reestablish what your mission is within your mind's eye. See yourself in five minutes and where you want to be.
Run the water as cold as it will go and fill. Do not enter until tub is above waist height. When you enter, your heart will flutter, and you breath will catch. Try to breath with the heartbeats and hone into the rythym of chaos you've just created. This is one of your door ways, use it quickly.
At this point one is able to enter the doorway while still in the bath, though extremely inadvisable due to high risk of drowning. If you can lock onto that chaotic frenzy, that door will turn into a key for later.