You are wishing to create a servitor, correct? Or are you just wanting to create a sigil for an existing servitor of yours?
The way i begin is meditating on what it is the servitor needs to do, it's function. I will write down a list of commands, like programming for the servitor.
Many servitors do not make it pass this stage, i abandon the idea because many intentions are not suited for servitors, and they are a huge undertaking and expenditure of energy.
So, for example a servitor for home protection.
I would command that it stays home, that it listens to any new instructions i give it, and let's me know if anyone is messing around while i am not there. The page of commands can sometimes reach up to a page long or more. Often times how the servitor looks will change from what you originally intended but that is the only variation in design i allow.
As far as the actual sigil creation there are many methods available, try using the magical squares like the kamea of saturn and English alphabet methods like Austin Osman Spare or engish translated to Runes. =) You can sigilise just the name of the servitor, especially if the name is a composite word of the commands, or you can sigilize each command and arrange them into a larger "Seal'. Do not be afraid to revise over and over again.
Do not forget to create a ritual of sorts where you feed your servitor energy regularly, or design it to be self-sustaining. Also giving your servitor a lifespan is a good idea, they can be tricky when it comes to dismantling them, so it is good to have an "off" switch.
A friend of mine, Andrew Martini, did a really good instructional video on servitors. He has a pdf that goes along with it. You can see the video on his YouTube channel. Here is the link:https://youtu.be/0XyTFLbf554.