Good point by MIDad. If the quorum is a specific number and that number is currently working, don't rush to change it. A percentage of membership usually isn't a good quorum number for parent groups because the relationship between the number of parents willing to pay dues and the number willing to attend meetings is fairly unpredictable. If your number is a percentage or isn't specified, it would be best to set it now.
Be careful about waiting until your membership drive is over before adjusting your quorum. Whether that's good advice or not depends, in my judgment, on what your bylaws say now about the quorum. If your bylaws say that a quorum is a majority of the full membership, or that a two-thirds majority of the full membership is required to amend the bylaws -- or if they don't specify a quorum, in which case common parliamentary law defines a quorum as a majority of the entire membership -- then it may be very difficult after your membership drive to obtain the necessary numbers to meet or amend the bylaws.
That's why I suggested checking your bylaws *before* the membership drive, and adjusting the bylaws first if necessary.
As others have said, you can set your quorum in your bylaws. It's typical to set it a bit below your typical meeting attendance. You want it to be low enough so you can get your business done but not so low that just a few people can set policy that might be against the wishes of the larger group.
Before adjusting your quorum, I'd suggest waiting until you've had a handful of meetings after your membership drive -- that will give you a better sense of how many attendees you are likely to have at meetings.
You'll need to check your bylaws. They should specify what constitutes a quorum at regular and special meetings. If they don't, but they do say that your organization is governed by Robert's Rules, then the quorum is indeed a majority of the total membership -- so if you don't have a provision in your bylaws specifying a quorum now, you should consider amending your bylaws *before* expanding your membership.
Next year we're planning on holding a membership drive to formalize and increase our membership. However, we know that many people may sign up for a membership but never come to a meeting.
What are the implications of that in terms of having quorum for general meetings and voting? If we have 200 total members and only 20 people that come to meetings, are we still able to vote on things? So if we need to revise our policies and it needs approval by a simple majority, is that based on the whole membership (101 votes needed) or based on the people at the meeting (11)?