Disclaimer: I'm gonna phrase things emphatically but I do not feel that this is the best route for everyone or that everyone should do this. Take what works for you, leave what doesn't.
The first step is to consider your emotional reactions in order to find your core values. A core value will infuriate you when someone else violates it, and cause you to feel great distress when you violate it. If you get angry when someone else fails to signal in a lane change, but you don't feel equally bad if you fail to signal, that is not a core value violation it's just an inconvenience. You can start with a list of things that infuriate or disgust you to see done, and then cross off anything that you wouldn't be deeply stricken with remorse if you did it. Include things you think are obvious, such as killing or torturing.
Once you have this list, go through and check for things that aren't values, but you have accepted as values because you were told over and over that there is a right and a wrong answer. You can tell these because violating these things usually causes no real harm - for instance, putting the toilet paper roll on where it rolls off the top rather than the bottom. These things that seem like values can also simply be leftovers from coercive education convincing you that it is wrong to mix up "your" and "you're" when in reality it's just not abiding by unnecessary dogma. However, you may simply have some problematic values. If you feel it is morally wrong to use grammar that violates the rules, then that could be one of your core values- it's just that your value shows you are an elitist. I would not recommend trying to strengthen such a value.
Next look for common themes. If your list includes shoving animals, grab-handling children, and hugging people without asking, there is a theme there of respecting bodily autonomy which is very important to you. Try to group your list into 8-13 themes, and then define these so that everything on your list is included. So, in this example, I would define the value for these three things as 'respect' meaning 'considering each being to be the only valid authority on how their body should be treated and requesting permission prior to any touch' and I could add to that definition if I saw other violations of respect on my list, such as pressuring people into activities or ignoring what they want. I might add "...and being careful not to infringe on their will."
The above part I did almost two years ago, and the below part I did a few months ago, then attached them in a booklet a few weeks ago. This has been a very long project!
Next, come up with a sentence or paragraph that describes the relationship you want with your value. Here's my template (if you want to use/modify my template for your own values that is fine with me; just don't copy my own specific values phrasing that I wrote on my cards).
In the name of [value], I contemplate [important things about that value]. I seek to [do an action that expresses this value] and [another action that expresses this value]. I question [aspect that contradicts this value] and check [something that helps me determine how close I am to my aim]. I seek [value], I create [value], I embody [value].
THAT was a really REALLY cool exercise for me. I feel like I gained a lot of clarity on my values by doing it. For instance, I realized that consumption is often the opposite of creativity for me, and to maintain my core value of creativity I need to be sure that I am not consuming too much of things that reduce my creativity (such as shows that don't make me think).
[photos and descriptions of the core value pages in my chant book]
[general image description: all of these photos show a long rectangle of handmade paper, white with bits of greenish brown stems scattered throughout. The papers have been perforated with a needle along the short left side and are attached as a booklet with thick waxed thread. At the top of each page in shimmery vivid violet ink is a set of symbols: magical lettering which I created for ceremonial use. The main section is in shimmery spring green ink, and then the last three phrases are in shimmery bright scarlet ink.]
In the name of justice, I contemplate all forms of oppression and hierarchy. I seek to uproot oppressive ideology and dismantle oppressive structures. I question my behaviors and check my assumptions. // I seek justice // I create justice // I embody justice.
In the name of growth, I contemplate my progress and seek to develop any mediocre skills and to cut out habits that prevent my becoming a more productive person. I question my habits and practice my skills. // I seek growth // I create growth // I embody growth.
In the name of creativity I contemplate my consumption and expression, and seek to create and share more than I consume. I question if what I consume will help me create, and I check for a balance. // I seek creativity // I create creativity // I embody creativity.
In the name of connection, I contemplate my place in the web of life, and seek to empathize with those near and far and to nourish my connections with all beings. I question my first impressions and follow my yearnings. // I seek connection // I create connection // I embody connection.
In the name of curiosity, I contemplate my recent sources of learning and seek to discover new knowledge and understanding. I question everything and check for new perspectives. // I seek curiosity // I create curiosity // I embody curiosity.
In the name of openness, I contemplate my sharing and seek to be vulnerable and offer sharing which will allow me to be known. I question my reticence and check for the edge of my comfort zone. // I seek openness // I create openness // I embody openness.
In the name of honesty, I contemplate deception and confusion, and seek ways to express and explain that honor truth. I question my hiding and check for clarity. // I seek honesty // I create honesty // I embody action in honesty.
In the name of action, I contemplate my risks and opportunities, and seek to take action in whatever ways I find. I question my stagnation and check for more chances. // I seek action // I create action // I embody action.
In the name of reverence, I contemplate the magnificent importance of all objects. I seek to honor objects in all my uses and to recognize their magic. I question my casual interactions and check my stewardship. // I seek reverence // I create reverence // I embody reverence.
In the name of respect, I contemplate consent and autonomy. I seek to avoid exerting unasked control over others and to avoid causing damage to others. I question my influence and check my effects. // I seek respect // I create respect // I embody respect.
In the name of thoroughness, I contemplate my recent projects and seek to do all I do to the best of my ability. I question my methods and check my work. I seek thoroughness, I create thoroughness, I embody thoroughness.
So then, after all this I recommend writing, printing, or recording them in a way you can keep with you. Try to read or listen to them daily with full attention, thinking about how they apply to your life right now.