If you are looking for the best way to be a spy without anyone ever knowing, follow along on the mission and pick up a few tips on how to trail someone as invisibly as possible.
It will help if you have another spy on your side so you can take turns when following someone. This keeps them from becoming suspicious. If every time they turn around you are there, it may make them begin to wonder if you are following them. You do not want that!
Dress accordingly. Everyone see spies as wearing a trench coat and sunglasses. Don't you think you will stand out in the crowd if you are wearing this get-up? A good spy is so average that no one even notices they are around.
Carrying a backpack does not look out of place and you can keep all your valuable spy equipment for each mission handy. Carry a cell phone. People standing around talking on cell phones have become so commonplace that no one pays them the least attention. One with a camera is an even better idea.
Here's the scenario. You are trailing the suspect and they are 'innocently' shopping. Fitting in to this scene means you can 'shop' as well. Look at the merchandise, but you are not really looking at it - you are watching your suspect. But, to an observer you would be just someone shopping. That is the key. Look as normal as possible.
Now when they go into a store you would look out of place in, you have to come up with another plan. For example, the woman you are following goes into a store or a section of a store that sells women's underwear. You are not going to want to go there if you are a male. But you can stick close by without being noticed.
Of course, you could always duck around the corner and put on your wig and female disguise (all good spies carry a variety of disguises) and then you can enter the store without looking suspicious. Or you can stand in front of the store with your back to the entrance, checking your make-up in your mirror which is really trained on the inside of the store so you can keep track of your suspect.
So you've taken care of one store, what about when she goes on to the next one? If you show up too many times, you might begin to be noticed. It's time to send your partner in and let them take over for a while. You can use this time to come up with another disguise.
For the quick change, wearing a couple of pair of shorts and a couple of t-shirts underneath your clothes allows you to just remove one set of clothes, put on your sunglasses and a hat and you have a totally different look. Of course, the weather needs to be nice for this outfit to look average.
Now you are ready to be standing by and pick up the trail again so your partner can do their quick change. Working together like this will allow you to follow someone all around and they will never notice it is the same two people trailing them everywhere they go.
This works well for following someone in the daylight hours, but what if your mission is after dark?
Of course, the clothing you wear is going to be important and be aware that people are more wary at night.
Practice moving as silently as possible and see how long it takes before you are around someone before they notice. You can use your family to practice this and see how quickly you can perfect your invisibility.
Come up with a plausible reason for being where you are. That way if you do get caught, you may not necessarily be following someone, you could be doing something entirely different. For instance, it you are on a dark street and the unthinkable happens, your suspect catches up to you and asks what you are doing, you will have an explanation. You may have dropped something or you are looking for your cat.
Following from afar at night is another way of remaining unseen. For this you can make use of night vision binoculars. This will get you up close and personal and your suspect will never know you are around. Find a hiding spot, preferably high up and staying put cuts down on the odds of getting caught. The secret to night spying is to practice your skills way in advance so you will have them just right when the time comes.