I have been reading of, and practising some internal
methods such as Yi Quan, meditation, and Chi Kung. I've
read and understood that as long as there is no mind
intent the practise should be safe. Chi Kung on the
other hand seems to use (often) mind to control the chi
energy in the body.

"Falun Dafa cultivation practise is free of mind-intent,
with no concentration, and is not guided by mind activities.
So practising Falun Dafa is absolutely safe, and it is
quaranteed that practitioners will not go awry."

-- from book "Falun Gong" by Li Hongzhi

(I don't actually train Falun Dafa, but I've read the book)

Also some discussions here at Kung Fu Magazine's
forums have impilied that you could "mess up" your
energy system by mixing methods too much.

So my question is: How do I avoid harmful practise,
and how do I choose Chi Kung exercises so that
I don't mess up my energy system?

Thanks.