Price things in your area so you know what you’re are possibly looking at per person and as a whole... then work on a budget...if you have a budget than you can see if accommodate a ton easily or if you need a short list
for actual people Family first Then start with VIPS and then friends/extended family and then co workers and acquaintances
Start with your dream list: put everyone on there that you would like to invite. Then compare that list to what you can afford and comfortably fit in your venue. Start getting rid of guests until you reach a desired number. It is hard, I personally totally stressed over the guest list, but it can be done.
I would figure out what your budget is for catering & alcohol specifically (if you plan to have a bar) and then get quotes for what the per person price would be. I personally know that it is hard to create a dream list of everyone you would want to invite and then have to cut people out so I have heard it is easier to figure out how many people you can afford and then start with your list with your inner circle and then build up to that max count.