One thing only thing stick it to the outside edges only none of the ribs
Generally I have read to stick the outside edges only, then shrink. Once shrunk you can stick the covering down to the ribs either by brushing glue or sealer through the tissue, or ironing down the iron-on coverings.
Here's an article from Bob Benjaman about tissue covering a rubber powered J-4 model. There are pictures with captions of each step starting part-way down the page. Most of it is probably review, but hopefully someone will find some useful tips or reminders in it.