Smell & sound are more important than people think.
If your a smoker, dont when your out, no aftershaves, antiperspirant, scented soaps, if your gear is freshly washed then just rub some leaf litter over yourself to mask it.
Turn your mobile to silent & turn vibration off, you'd be surprised how many calls come just at the wrong time
Camo clothing helps but only when its matched to the terrain, mossy oak/real tree hardwoods is great in woodland but out in grassland you stand out but in general you can get away without going out looking like your on an SAS mission, its just common sense really, no shiny things, keep low, wear dull colours (browns, greens, greys)
when stalking anything keep downwind of it, that means you ideally want the wind blowing towards you, not away from you.
I was lucky my father taught us country craft and how to sneak up on critters when we were kids, he once managed to sneak up on a deer and tap it on the shoulder.. it took off like a missile!!