I have been buying bitcoin when the price was around 400$-450$.Most of my bitcoins are bought at that price around 40 BTC and remaining at less then 600$ price.i have been holding btc in paper wallet since then and already my stash in usd is 6 times.
here is one of my tx

what i want to know is please suggest some ways to invest my bitcoin at zero risk to earn some profit.Even 0.8% to 1% profit per month is good for me but it should be risk free.i don't mind the profit percentage but risk should not be there.if you have some suggestions please post that too,if i should keep holding for more years and if yes how long should i hold?
I think its better to hold onto your bitcoins although its not risk free, you can still also earn from it. If you really wanna invest go for ICO's that has a good project and vision. Research very well so that you can earn profit many times more than usual.