There are two things you can do to get the most value out of your next onsite visit with a service engineer. The first is to make a detailed list of issues. A list organizes your needs, helps ensure you are not forgetting anything and enables the engineer to prioritize what needs to be done. It is a great tool to help identify if there are other coworkers who need assistance as well. You can email this list to our office (firstname.lastname@example.org) prior to your appointment or hand it to the engineer when he gets there.
The second is to sign off on the work completed. This is really for your protection. Before the engineer leaves, you should look at what was done and make sure everything you needed has been addressed. It is also important that you understand how to use any upgrade or new functionality. It is not a good feeling when you come in the morning after an engineer was there and you turn on your computer and something appears to not be working because it is different. The best way to avoid this is to take a few minutes to approve the work while he is still there.
There will be times when you will just not have the time or resources to be able to do these things, but keep them in the back of your mind. When these steps are done, it makes for a very positive experience.