First, the fact that they gave you their details means that you are at least PARTLY expected and it's not some horrible cold call so you're half way there already.
I think something like,
"Hello Mary, this is Lifeinagoldfishbowl, we met at [insert name's} vie cosmetics party. How are you/how are your DC/appropriate friendly question that you remember from when you met her but only one. You suggested you might be interested in hosting one of these parties so I wanted to ring you and see how you were feeling about it..."
Agree with OhBling - they've given you their details, so it's not like you're hassling them - in fact, they may be thinking "Why hasn't goldfish bowl rung me yet?"
And if you can't think of a good intro question - just go with 'Are you enjoying your summer/have you been on hols yet" or some other seasonal comment
If they expressed interest in buying rather than doing a party "I know you were interested in knowing some more about xxx/were considering putting an order in for xxx - is now a good time to talk about that?
You don't need to go all pushy-sales person - but do stand up & smile when you call - makes a big difference, believe it or not!!
I agree with the extra comments from deep except I personally HATE it when people ask me random questions for the sake of it. If you don't have anything specific, I'd launch straight into ,"I know you were interested in... is this a good time". Or something similar?
Or, make a comment on the party you were at eg, "I really enjoyed Mary's party - the food was great/the people were lovely/etc"?
Fair point, bling - it also depends how comfy you are with random chat! I random chat for a living (sort of) so am always happy waffling at people - and often find that it helps with a bit of bonding (Ohh, yes, I can't wait for the end of the school hols too! type stuff) BUT agree that it can be a bit hairdresser-y
I would get straight to the point and save the chat for later in call when you've established recipient is friendly eg 'hello it's goldfishbowl here, you'll remember we met at X's party. You said you might be interested in x so I thought I'd give you a call to see if that was still the case'. Then pause to give them a chance to speak etc etc. Have a smile on your face - it will show in your voice IYSWIM.
Perhaps you find it difficult because you are worried that they will have changed their mind, and will say no.
Rather than asking them if they still want to hold a party, or buy something, why don't you try something like this:
"hello it's goldfishbowl here, you'll remember we met at X's party. You said you might be interested in x so I thought I'd give you a call to tell you about the special offers we have on at the moment.."
This can get you into a conversation without asking for a direct yes or no answer.