The best place for beginners would be Route 5 with that huge patch of Purple Flowers. Flowers are easier to see than grass cause they are a bit taller. You can chain Furfrou Abra Pancham Skiddo Smeargle Gulpin or Flabebe there.
Route 7 has decent grassy patches along with Route 16 near the Fishing Shack. Try using a Magnet Pull Pokemon and chain Klefkis.
Edit: I have to say... there must be some merit to this 1st hour of Friend Safari shinies or first 3 encounters anyway... I have gotten so many legit shinies from there, it isn't funny. Let me write down the shinies I have encountered since I started using it.
Noibat - 1st encounter! I was so blown away, I had just unlocked my friend's safari!
Spritzee - Trying to find Floette or Kirlia, found this instead within 300 encounters, although 120 at night before bed and then about 150 while riding the train to work and I had shut my game off in between.
Pawniard - 1st encounter! I was just looking for a Liepard to catch for the Pokedex!
Spritzee - 4 encounters. Tried my luck again for Floette and Kirlia. Nope. This time it was male.
Charmelon - ??? encounters. Was using a Male Cute Charmer for a female Braixen and got a female Charmeleon found this within an hour.
Braixen - 1st encounter! Surprised but slightly disappointed not finding Braixen I went into a new Safari with had an unknown 3rd just revealed and it was a female Braixen!! And this was 30 minutes right after Charmeleon!
Quilladin - ??? encounters. Within an hour. Tried to look for Oddish or Petilil but got him instead.
Duosion - ??? encounters. Found it within an hour looking for female Espurr using Cute Charm.
Gothorita - ??? encounters. I don't remember if I found this in the same safari as Duosion or how long it took. Luckily it was female and had Shadow Tag!
Abra - ??? encounters. Within an hour after Gothorita, changed Safari to a newly added one with Espurr to avoid a shiny Drowzee (Blech). I was about to use a Master Ball but relized Gothorita had Shadow Tag to prevent that sonuva b**** from teleporting. Super lucky! ...except Cute Charm was still active so it was female...
Espurr - ??? encounters. Found within 3-4 hours or more. Took forever and didn't think I would ever see it but kept persisting. She eventually showed herself and is the longest hunt I ever did. I almost hunted on a second 3DS to see if a shiny Espurr would pop up in the wild on Route 6 since a lucky guy found one in 3 encounters...
Metang- 50-60 encounters. Within an hour. Well I wanted to find a cool shiny for my brother since shinies didn't seem like they were popping up in my game anymore and I wanted to see if he would get lucky in Y. My brother's game doesn't hand me shinies out like my X so I had bad feeling but I wanted to give it a try anyway. I was amazed how fast it took to find this shiny. Also: the 3rd Pokemon is not unlocked.
Garbodor - 6-10 encounters. Just exploring a new safari during the age of Instacheck and this popped up! He had his hidden ability too! But. I didn't save sooooooo... when I accidently released a shiny Skiddo I just chained I had to make a choice... risk the soft reset and hoped I had saved or lose the skiddo I wasted so much time on. I reset and no more shiny Garbodor...
Tyrogue - 1st encounter. Tried to find that shiny Garbodor I just lost but after an hour I gave up and went to explore the next Safari to see who was the 3rd Pokemon that was just unlocked. WHAAAAT. You give me a Tyrogue when I wanted Garbodor back? Oh well, it was still really cool. I evolved it into a Hitontop but it looked gross, and then Hitmonchan but that was even worse and finally Hitmonlee which is sort of cool, but it wont ever get used since it's... Modest.
Teddiursa - 30-50 encounters. Within 40m to an hour. After the fall of Instacheck, I wanted to thank Ninox for checking the SVs for my eggs and allowing to get Carbink, Binacle and Honedge. I wanted to repay the favor with a shiny she wanted. However Teddiursa was not popping up in my X and the one I bought on eBay (yea I decided to spend money on a shiny...) wasn't ever gonna get sent I turned up the pace and started hunting on 2 3DS for a shiny Teddiursa. Although in X it seemed like it was never gonna get the shiny Teddy bear when I least expected it, it popped up my brother's game. Guess his game isn't that unlucky. Afterwards though I never saw another shiny for a couple of weeks.
Helioptile - 6 encounters. Well bummed out and after a drought of no shinies for weeks and no sign of Garbodor ever returning I was thinking that it was time that my luck finally ran out. I started chaining again and after a successful Drifloon I went to the safari to see what Electric type was revealed. Within 6 encounters I found a shiny Helioptile. Could my luck be returning?!
Oddish - ??? encounters. Within 2 hours. Wanting to test my luck again I went to a grass safari to get that shiny Petilil I wanted so bad. Got him instead. Wanted a female and Cute Charm failed. But I turned him into a Vileplume.
Oddish - ??? encounters. Within 20 minutes after the last shiny Oddish in the same Safari! Another popped up! And it was female! Happily turned her into a Bellossom.
Shelgon - 5-10 encounters. Was just messing around and did not expect to see a shiny so soon and this was in Kaiser's safari!
Garbodor - 1st encounter! Finally reclaimed him after adding multiple Poison safaris and switching between each safari within 30m to an hour so this went on for a couple of weeks as I was exploring every new Poison Safari and I spent at least 2-3 hours hunting a day. I finally found him on the first encounter. Too bad he didn't have his hidden ability but it's not like I was gonna use him anyway.
Fraxure - 1st encounter. Wow. I was training my Pokemon to evolve for the Pokedex and I said to myself "yo you should train in the friend Safari even though it will be slow, you might find a shiny!" Although... about 8 hours altogether within 3 days I didn't find any shiny. But I hit traffic on the way to work and parked in a garage and took the T and pulled out my game. 1st encounter was a shiny Fraxure. In Kaiser's Safari again. WOW.
Ahem... sorry for the wall of text but I wanted to be as insightful as possile for anyone trying to research the ratio of Friend Safari Shinies.
As of right now I have encountered about 21 shinies from the Safari. The only 1/4096 full odds shinies I have are Klefki and Beedrill. Most of them took less than 30 encounters but there were a few that took persistance.
Sometimes within an hour I will soft reset the game. Sometimes I switch safaris within an hour. Sometimes I just start up the game and it just gives me a shiny. I hope this was helpful despite my blabbering and excitement from finding these shinies.