Firstly, the word "summon" seems like a lighty thrown around term. You can't simply just summon. I reccomend for you to start with invocation. An invocation could be a complex prayer of asking the diety for it's presents, or a simple, polite,"Hey there, could you come here for a second if you've got some free time?"
I've also heard that to summon is very rude and is demanding the presence of your deity, which you won't want to do.
To be honest, Hekate isn't really much of a people person. Originally, She is a Titaness, and was not happy with Zeus when humans were created. So to be asked to come to a place where She didn't want to be, She might not show up or show any signs that She's near.
If, in fact, She was interested, try a simple offering or prayer. Normally deities tune into you at the smallest mention of their name(s), and I wouldn't want to waste Hekate's time.