1) Have a high DexNav Number. I usually start searching around 30 to reliably get items.
2)Have repels. I actually found that using the D-Pad to face in a different direction, but not move from the same spot actually counts as movement of 1 tile (with regard to the DexNav), so you can feasibly change direction, then hit the search button again.
3)
http://www.reddit.com/r/pokemon/comments/2nnrsa/qa_dexnav_chaining_and_shiny_pokemon/
What's confusing about this is that it's not really chaining based on what people say. Locormus stated that they caught a *Poochyena at 15-20, while it has taken others 120+ to even encounter a Shiny in this way. Some have hit in the middle, and some haven't found one at all. Based on this, it seems like a set % is used in the Dexnav that boosts the rate, as even with the 23 friends used in that experiment, it hasn't been proven that actual DexNav chaining increases the odds until it reaches a rate of 100%.
What I would like to see is testing done WITHOUT the Shiny Charm for numbers, and then WITH it, to compare.