I don’t mean in an intellectual or logical sense.
Take a moment to think about the good things you have. Bring this state of mind in your daily ventures. Notice more good things you have not thought about before. Imagine life without. Think of people living without them. Appreciate that you have them.
I’m not sure I completely understand the question. It sounds a bit like “How do you enjoy a nice meal” - there’s no way to instruct someone how to appreciate or enjoy something, you just have to take a moment.
The thing with the “before it’s gone” part is that we don’t always know which things are temporary, so you just have to cultivate an attitude of appreciating things in your life, including the people in it.
Just as tasting food mindfully teaches you to distinguish its flavors and ingredients, engaging in activities you enjoy teaches you to relax and appreciate them more deeply.
Just think what it would be like to lose it right here and then. This is what works for me.
Imagine you never had it in the first place and how that would make you feel now