When I first started quilting, I had an unfortunate experience of having friends decide to help me build my stash. At the time, I thought it was a great idea but in the end, their ideas of quality fabric and my ideas were two completely different ideas. I ended up with almost one hundred fat quarters that I did not know what to do with and they ended up being used for a nine patch quilt I made last year to stash bust and restart. That said, if anyone tells you they want to help you with your quilting, I would give them a small list of tools - rulers, cutting mats, pressing mats, things of that nature and tell them you'll pick your own fabric and thread. It will save you time and a lot of space.
I would look into getting fabric bundles - jelly rolls, fat quarter bundles, layer cakes, even honey buns. By using those, you'll be able to find out what fabrics you like to use, what the colorways and values you'll lean to most and it'll allow you to sample an good selection of the collection in one shot. I've been finding myself getting into the deep jewel tones lately, I never would have considered those years ago, so keep an open mind when you fabric shop and realize that your preference may shift a few times over the years before you finally settle down and decide what's pleasing for you to work with.
Online shopping definitely has its big pluses, places like Marshal's Dry Goods always have fantastic sales and clearances going on and it'll save you some money in the long run. I just bought a full bolt of unbleached Muslin several months back for only $37 - when you consider that the average price for it per yard is upwards of $3.50/yard and the bolt I bought was a 50 yard bolt, you see how much money I saved. I now have more than enough Muslin to make a lot of quilts, depending on how much background fabric I need per pattern and learning from my first quilting go-round, I had a ton of fabric, but zero background. And when you figure that the majority of the quilt is the background fabric, you'll be able to shop for the rest of the fabric for whatever quilt you're working on with a free mind. I'll be buying a bleached Muslin bolt sometime this year, I have to get over my phobia of working with pure white fabric somehow, lol.
Consider keeping a 'stash journal', this is something that I wish I had done back when I had so many fat quarters. When you buy fabric, write down everything about the fabric, who manufactured it, where you bought it, how wide it was, how much you spent, etc. You may come across a fabric that you want to use later and when you find out that you don't have enough, you can track down that fabric much easier. I keep receipts in my journal just to be safe, but writing all that down will be a lifesaver if you can't find your receipt. The more information you keep, the better your chances are if you want to revisit that fabric later and you're not able to find it in a fabric shop. If the selvage edge has all of the information on it, when you cut off the selvage, save it and add it to the journal, too.
Last thing I do is that when I'm buying fabric by the yard and I've fallen in love with it, I'll add up to three yards more to what I need for the pattern. If it's ridiculously marked down because it's on clearance, consider buying the full bolt. Also, check with the shop that you're in, they may have bolt discounts, at least places like Hobby Lobby and JoAnn's used to have them years and years ago. Check for incentive plans, if you buy online, too. The gal I get my hand dyed fabrics from has what she calls a 'Frequent Dyer' club. As soon as I get ten yards of fabric from her, she'll custom dye up to a yard (I think) for me for free. Local quilt shops and small businesses sometimes run those kinds of deals to keep you coming back as a customer. If you're happy with what you're getting from them, sign up because that will save you money in the long run, too. And the more money you're able to save, the more fabric you can buy.