This is an updated post based on some tips I gave a few years ago on how to make a pact that works - it doesn’t look at the mechanics (written in blood or ink, parchment or paper, Full Moon or New) but instead focuses on the human psychological & emotional side - for that reason, it also applies to spirit marriages, and making lasting sexual contracts with spirits:
To make a pact that will be successful and beneficial for both you and the spirit, you need to understand what your own values are, what your weaknesses and strengths are (if we’re honest, they’re often two sides of the same aspect - my core intensity can be self-destructive or excellent, depending on how conscious I am of deploying it, and what direction it goes in), and have a good understanding of that spirit’s agenda and long-term aspirations.
And even if you come at this from the point of view that spirits are archetypes in the mass sub-conscious, or powerful channels within your own mind, this will still hold true – any spirit that substantial will have habituial ways of acting that are unlikely to alter on your whim. If you want something that changes to suit you, create a thoughtform, don’t expect a spirit known from before you were born to change on a dime.
Things to look for and be completely honest about are situations from, for example, your childhood that you think you “should” be over or be able to cope with now, but in reality, can’t – this is because if you “should” yourself into trying to do things, you’ll risk pushing really hard on things that look simple on paper (or in theory) but then burning out when it becomes too hard.
And the spirit may love you, protect you (often like a child) but they cannot always easily relate to the finer points of human weaknesses, and even if you feel certain your spirit is different, erring on the side of caution before finalising a pact makes sense, because you can adjust the terms in their favour later and they will not argue against this.
There are things that sometimes undermine us on such a deep level, by happening in times or situations where we were powerless, that the moment they’re factored into any task that reminds us of them in some way, it weakens us like our own personal Kryptonite, and the simplest task becomes harder because the background situation creates its own problems, and drains away our energy and feelings of power.
We all have baggage and flaws, and for this to work you need to ID your own, with clarity and self-compassion, and then ringfence them as things to either be left alone, or led at your pace.
Get ready to make lists, maybe in a word processing document you can delete securely, or burn afterwards, because getting things in writing can massively assist you in achieving clarity at this stage.
And on the flipside of this, work out what you really don’t have any problems with as well, and that again may not be something your everyday-world self wants to think about too much, you might for example have far less of a conscience in some matters than it suits you to pretend in everyday life.
- If in doubt, put in more limits than less, and then you won’t be under too much pressure and can grow into the person you wish to become whilst not having to struggle to keep up, and that way you don’t risk the spirit feeling cheated or let down.
I’m not saying you should keep any limitations intact and dance round them like they’re sacred idols, but just make sure you’re not going to end up irrevocably broken by being given more to handle at once than your human psyche can deal with. I’ve seen this happen to people and it’s not good, not a “trial by fire” - more like getting steamrollered (and that wasn’t even with “demons”).
This is my experience anyway, and how I’ve formed pacts that have worked well - don’t worry about what the spirit ought to understand about you or what they can, just get those things down in black and white so there are no mishaps further along the line.
This approach has worked well for me, and if it resonates with you, perhaps it will work for you as well. 
