Networking is about getting to know people, making contacts and building relationships. Once you've made contact, that's only the start. It's not a one-touch, one-way process. It's something that will develop over time.
Many people go to networking meetings - just gather up the business cards, put them into a pile, may or may not add them to their mailing/spamming list but that's probably the last contact they have until they meet them at the next meeting.
So, in order to make your networking more effective,
... send a personal message, talk about something you discussed when you met or something they mentioned, share some useful information.
... arrange to meet up and find out more about each other's business and what you can do to help.
... send a generic message to every attendee - with a sales pitch.
... add everyone to your mailing list by default without asking first or giving them the option to subscribe or unsubscribe.
Network, connect and re-connect ... often.