Where do I get my yarn?  
For the majority of my patterns I try to use a yarn that is good quality, washes and wears well, and is readily available.  My favorite acrylic is Vanna's Choice, it's soft and readily available in most hobby stores.  I also will occasionally use I Love This Yarn (Hobby Lobby) but I have to check my gauge because it crochets a bit smaller for me.  As for delicious hand spuns...well, I am not completely committed to only one supplier, but I do tend to stick with a few and order from others from time to time.  I mean really, there are so many amazing fiber artists out there with so many delicious yarn choices I can't commit!  You can find tons on Etsy, Ravelry, ArtFire as well as on .com sites.  When looking I typically search with words such as 'handpun', ‘thick thin’, ‘thick and thin hand spun’, ‘hand spun merino’ etc...  I am totally obsessed with 2 ply worsted or dk weight hand spun right now as well!  
Remember Google is your friend.  Search it, you’ll find a ton.
The main shops I order from regularly are:
Debra of Winding the Skein, facebook
Dee of HeartstringsbyDee, facebook
Ny of ilashdesigns facebook
Shannon of Grand Vally Fibers, facebook
Lynn from FuzzyFibers, facebook

These women are incredibly sweet and supportive.  Fortunately for them (and a little unfortunately for me) they are all very busy and tend to sell their stuff sometimes before it even makes it to their shops.  If I am shopping from Dee or Ny I always search their sold orders and luckily for me both women are typically happy to spin more of something I want.   Fuzzy Fibers really doesn't do custom orders and uploads a few times a month.  Her upload date is in her shop announcement...get there on time, her stuff sells fast!  You can't go wrong with any of these ladies!  For the clown I have purchased from Shannon at Grand Valley Fiber.  This is the only place I have purchased yarn for the clown hat so far.
I have tried a few others and been happy as well.  I do tend to only order one my first time to be sure that I like the product without a huge investment.  Nothing worse than buying a ton of yarn only to get it and have it be smaller weight than you thought or to smell like smoke or other stinky stuff!  

{Sidenote:  I have not received any perks from these shops I just love their stuff and like to have shops to send you all too!  That being said I have no problem accepting free yarn in return for my opinion shared here :)  soooo if you want to send me some feel free}
How do you get professional pictures??  
In my opinion photos are the second most important thing to selling well, only behind selling a good product.  How do I get professional photos?  A lot of people will have a different answer or recommendation.  My best advice is to do what works best for YOU.  What works best for me or for someone else may not be best for your shop.   
1.) Trade:  I think this is the most common way people get photos, it is also the most common way to get screwed over.  You send off the item to a photographer in exchange for a few photos of the item.  Typically this is a straight trade, item for photos, no money.  Typically these photos will be watermarked.
2.)  Photographer discount:  offer items at a discounted price in exchange for final photos.  A lot of people will discount a % or the complete price after receipt of the photos.  This is probably the safest route as far as not sending an item out and never receiving pictures but you’d have to find a photographer willing to pay up front.  
3.)  Pay for a shoot.  Don’t have your own models?  Ask your photographer if they know anyone?  Ask friends and family members if they know anyone that would be willing to model.  I have even posted on facebook looking for a particular age/look.  If you are paying full price for a shoot be sure you have a decent amount of items you want shot at the shoot.  I would not expect these photos to be watermarked since you are paying like any other customer but you'd have to check with your photographer as this is likely considered a commercial shoot.
Talk to your family photographer, they may be a great match for you.  Look on Craigslist or other community forums.  Typically (but not always), these are people just starting out, building their portfolio, etc... and more likely to be willing to work with you or even strike a deal.  Be sure to always check their work before contacting or committing to someone.  They may email you asking to trade, you’re excited and race to the post office only to see their work later and not like it at all!  In today’s world so many people think they are photographers and may not be to that level yet.  The first time I work with a new photographer I would only send 1-2 items the first exchange.  Again, you want to be sure you like their work and that you actually get pictures back and in a timely manner.
The main photographer I work with is Ciara Hammonds of Ciara Hammonds Photography.  She is awesome to work with and has become a great friend to me.  Pretty sure my son is in love with her daughter and who could blame him?!?!  You can check her out on facebook, her website, or her blog.  If you are in East Texas check her out!  You won’t be disappointed.  

I have just started working with Jenn Hunter Photography and couldn't be happier!  She does amazing work!  You can check her out on her blog, facebook and website.  If you are in Plymouth, Indiana give her a call!
I also work with Rachel of Sugarshots Photography.  She not only photographs, but crochets her own items.  Rachel is much more brave with color than I am...I always look forward to her items and what she has created for them.  You can find her on facebook, her website, or her blog.  If you are in Connecticut she is a must!

How did you find selling success?
Hard work.  No seriously, a lot of blood, sweat, tears, sleepless nights, sacrifice and money went into getting my business to where it is.  My family has been very patient with me.  I started IH when I was working full time and had a new baby.  I had little to zero knowledge about selling online.
Do I know everything?  NO 
Do I fail?  YES 
For the most part I have had to learn as I have went along.  Google is my friend and should become your friend too.  The internet is an amazing tool and can truly provide you with almost anything you are looking for.