I get asked a lot about the differences between process service and investigations. While thaere are many differences, there are similarities. Sometimes to find the person to be served, you need to do some investigating yourself. You may need to find where the person lives, works and hangs out. The reason is you may need to serve them where ad when you know you can find them.
Process Service is 99% about being in the same place at the same time as the person you are serving. This is easy enough when you have cooperative folks, and can be very difficult when people are trying to avoid service. Sometimes you need to learn a prson's schedule and habits. You need to learn about the vehicle they drive and may need to get a description or photograph of the subject.
One more similarity is surveillance. There are those pesky serves that can only be done with surveillance. You simply need to wait un noticed until the person eing served is leaving or arriving from a place you know the will be.
Since serves have a set fee, you usually need to get permission from the client to charge for "wait time" if you are going to conduct surveillance on a serve. Otherwise, you are costing yourself money if you are doing a serve. I know a lot of servers out there, myself included a time or two, that just get fed up with the avoidance that you make all sorts of special efforts to make the serve. Sometimes it is just a matter of pride.
Whatever you do - stay safe!