A problem with the approach you want to take is that you will most likely will receive a lot of qualitative feedback - and it takes a lot of time to evaluate and assess qualitative feedback. Another problem with an open file is that everyone can read what has already been written. This can lead to Groupthink and Group Polarization, meaning that you can lose some critical and valuable feedback.
However, relying only on quantitative feedback will not be a complete success either. The best approach is to integrate both forms of feedback to get deep insights into the workings of your community.
If you have a forum or another platform allowing an open exchange between users and you, a first step would be to start a thread like "What is the one thing you miss". This enables you to get a first overview of some points that your users miss and would like to see implemented. Additionally, you can put the following rules in place for this thread:
- Only one item per user
- Only name items once (duplicates disallowed)
- Vote for items of other users that you also miss (if a functionality to vote is provided)
These rules make assessing the things that are missed way easier as you don't need to read duplicate posts. If there is a functionality to vote, you can assess even more easily: users help you by showing you what features are very important for a large portion of the community.
This approach helps you to win some first insights without spending too much time on it.
The next step is to gain some quantitative insights: numbers. Create a survey on an external site (more on that later) that asks about some key points of your community. Questions could include:
- How much fun do you have in our community?
- Are you satisfied with the moderation of our community?
- Would you recommend our community to a friend of yours?
- On average, how much time do you spend on our website?
With these insights, you get a quick overview about the perceived quality of your service. Questions like these are evaluated very easily and fast, meaning that you can continuously ask for this kind of feedback without losing too much time.
You might be wondering now why you would use an external site to host your survey. This can help you getting more reliable and valid data as users perceive an increased anonymity on an external site. Some users, who want to give you a critical score, might feel discouraged to do so if the survey is on your site as they could think that you could somehow track how they reply, meaning that they fear repercussion.
By now, you should have quite a handful of data. You have qualitative data where users were able to write up precise ideas as well as features and you have numbers allowing you to get a glimpse of the perceived quality of your community.
If you implement a proposed feature, you should also add an item in your survey asking about this specific item, so you can see if the feature is well implemented and does what it's supposed to do.
Onward to the part where you motivate your users to give feedback.
You see, one important thing is that most users won't do anything if it won't give them a benefit. You might say: "Hey, giving feedback helps you in the long run.", but most internet users tend to be quite short sighted here: the internet is fast, so if I'm bored in your community I can quite easily join other communities.
So in order to get a lot of quality feedback (not just users clicking around your survey), you must somehow reward your users for reading your feedback thread and filling out your survey. Most communities and services have a feature that allows users to show other users their seniority. Oftentimes, these features are simply points collected or ranks achieved.
In the case of points showing your seniority, you should check if it's possible to automatically award points for filling out your survey. And if it's possible to award less points for these people taking significantly less time as others to fill out the survey, indicating that they just abuse their mouse and be done with it.
Another incentive could be introducing a new rank (or however you might call it) which is awarded for contributing quality feedback regularly. This rank could, for example, be associated with the deed of collecting feedback, meaning that the users, who contribute regularly, are awarded with the trusting task of collecting feedback of other users or motivating those to give feedback.
And don't forget: if the shown ideas don't work, ask your users what could work.