Think about it openly and critically. Name some activities that help you (and others) maximize spare/idle time---whether it be making money, losing weight, pursing a worthwhile hobby, etc.
I think spending spare time to learn new things or create new useful things will be great. Also spending time with family and friends will be very helpful specially to unwind or relieve stress. It will depend on what things will make you happy and satisfied spending your own free time.
I think, it would be different for each person. Some people would use their free time as a creative outlet and paint, while others would play on a softball team. If a person gains something that will make their life better, then it is time well spent. If the free time is spent boozing it up and doing things that will tear apart your family, it is a mistake and a poor choice of the free time.
Yes, I also think that reading is the best way to spend my leisure time. It is enjoyable and no matter what material I read, I always learn something new from it. It can help me sleep faster at times too so it has a lot of benefits to me.
The effective use of leisure time differs for each person. Some people feel that cleaning the house is a good use, I disagree. That would seem to be work. But others would disagree. What a person does during their leisure time periods should be something that gratifies them, that which makes them feel that they have done something, either productive or that relaxes them and reduced their stress level. Whatever choice one makes, should be conducive to self-gratification of the sort, that satisfies that individual. I write poetry, and other things, I also paint oil abstracts and draw.
Constructive or beneficial leisure time is when what we are doing can still be helping us grow as a person and never make us go backward. In other words, we should scrutinize if the way we relax or get entertain can have some side-effects against our health and well-being. For instance, spending time and money getting intoxicated with alcohol and smoking would certianly not be good for the body so that could never be considered to be a constructive way of spending free time. On the other hand, a person who is using his available time learning new skills or volunteering to do charitable works can be assured that he is enriching himslef with the process and for sure he will see benefits sooner or later.
During my spare time, it is either I am reading books or spending time with my loved ones. I usually spend my time working and that's my daily routine. Of course every once in a while, I should refrain myself from working hard and start to relax for a bit.