In some cases you will be able to act on a suggestion straight away. If so inform the employee immediately what action you will take and when that will be done. That will show your support for the employee and encourage improved performance.
If you can’t make a decision immediately, or you need higher approval for it, explain that you need to consider the matter further but be specific about when you intend to get back to the employee.
As soon as you have got a decision inform the employee of the outcome, particularly when you decide you can’t act on the suggestion. If you can’t follow through with the proposal, explain how the request was considered and why it can’t be agreed. That will assist to maintain improved performance.