Hello,
There is no such thing as strengthing chi, technically, Chi is a life force that will purify, improve and then develop itself.
How to realise effects of chi ?
-Close your ears with your palms feel the buzz.
-Stop for 1 moment close your eyes, just still your mind for 1 sec, you will see someone/something looking at you, its another aspect of your chi (aura).
- breath gently, half close your eyes and concentrate for 1 sec, you will see some dizzling in your body, that is the chi flow.
Someone above talked of Jing

, well if you simply cultivate and harness chi it will balance everything else.
How to strengthen -
- Pick any one thing, tai chi, kata or any other thing, just do it with breath sync , after some days/weeks/years you will get the power of chi developed to the full potential depending on cleansing of meridians.
Different people have different styles and learnings, diff. experiences, rather then asking people ask yourself , you will get the answer to strenghten chi and develop yourself. You are your best guide.
rgds