It can be fiddly work, tying line to a plant to attach onto bogwood or decor.
By the sound of it, seems you're trying to tie java fern to bogwood while is in tank?
If so, much easier if you take bogwood out and place on a table, having an assistant to hold the plant while you tie the plant onto bogwood would be very helpful.
Otherwise, no particular easy way except patience and perseverance.
One other thing you could try, is to superglue the plant onto bogwood.
As long as superglue is 100% cyanoacrylate thats should be fine for aquarium use. Do bear in mind to be gentle with the glue as can turn out to be a messy job if try to rush this.
And also, don't cover the roots of plants with glue, just small sections of the plant onto the wood seems to work best.