One of the great things about the web is that sites can be updated quickly and easily. This means that you can provide information that is up to date. The downside if you are the webmaster is that this also makes your job a lot harder. You really can't just build a site and leave it alone, you are going to have to make sure that you keep it up to date. This can turn into a very big job on some sites and may actually require a full time person to do it.
The most obvious thing that you are going to have to do is to make sure that you keep the content on your site up to date. If you have information that is posted on your site that is no longer accurate you are going to have to get it fixed. One thing that you are going to find is that as you are adding new information to your site it will have a tendency to grow unless you are very thorough about removing the old information. You can of course leave the old information up there if it won't be misleading for your visitors and there are advantages to doing so, particularly with search engine optimization.
The other big thing that you have to be aware of when you are adding and subtracting content on your site is to make sure that you also keep your navigation up to date. You have to make sure that you add links in all of the appropriate places to get people to new content that you have added. You also have to make sure that you remove the links that go to content that you removed. This can be tricky since a lot of the time you will forget where these links are. It is important to keep a map of how your site is laid out and linked together so that you can find all of the links that need to be fixed. This will make your life a lot easier.
The other big thing that you are going to have to deal with is the links that you have going to other sites. All of the websites that you are linked to will doing the same thing that you are, adding and removing content all the time. That means that some of links that you have from your site will go to content that has been removed. You have to make sure that you fix these links or your visitors are going to get irritated. This can be a very frustrating job since you will likely have a lot of links on your site and have no way of knowing when content is being removed from other sites, you are going to have to check frequently.