What To Upgrade First on First Road Bike?

depends on what your goals are i guess.  you stated you are doing it for fun, so i would spend the money towards something which helps you enjoy your time on the bike more.  most likely that would be apparel which makes you more comfortable.

The first thing I would do would be to get a fitting and positioning done. Nothing else can improve your performance as much as optimizing fit and position.

It's a tough sell because it isn't shiny, doesn't come in a box and most people don't understand it.

The man ^^^ is never wrong. 

Save your money for a better complete bike later down the road if you still feel you need it.  Buying components a la carte is very pricey.

The Giant Avail 3 looks like a very nice bike.  Unless it doesn't fit, I see no reason why that bike won't last you 10-15+ years.  

Like Tom mentioned, the first thing to do is get fit by a certified fitter.  Second is to make sure your contact points are right for you (saddle, shoes/pedals, handlebar/tape).  Your fitter will be able to assist you with this.

If you're having trouble with the shifting, bring it to your local shop and have them take a look at it.  Most of the time these issues can be corrected quite easily.  They can even show you which gear combinations (like being in the big ring and big cog at the same time) to stay away from.

x3   get a tuneup.  A good wrench will have your Sora system shifting perfectly.

after that- if you want to treat yourself to a little bike accessory... how about a nice pair of Continental Grand Prix 4000S tires?  Or, maybe the Michelin ProRace 4's.  Faster tires WILL make you faster (albeit, not much). 

Or, if you want something for free:  Download the Strava App on your phone.  It'll change the way you think about every climb.

I assume you already have clipless pedals and shoes.  If not, move it up to position 2 on my list.

Thanks for the responses so far. My LBS includes a bike fitting with the purchase of a new bike, and first tune up free. I've done both.

I do have clipless shoes and pedals, spd. Do shoes make a difference? I've only ever had this one pair, that I bought for $35 on a close-out because I have small size 5.5 feet and that's a hard sell. I bought them originally for spin class but got bored of "cycling" indoors.

Thanks for the suggestion of picking up gently used 105/ultegra shifters. Is this common? Where do I look for such a thing?

I agree that piecing a bike with components is probably expensive down the road. Instead of componentry upgrade, would I be better served buying a fluid trainer and trainer tire? I live in Vermont, so...not a lot of riding in the winter.

a fluid trainer is the best thing you can buy if you truly want to put in the effort and get faster and more powerful on the bike. i've had mine less than 2 months and already have seen big gains.  a lot of people have hunted craigslist for a while and picked up a $200+ fluid trainer for $60. 

not all shoes are created equal; my first cycling shoes were a cheap on sale pair like you say you got. later i got a $200 pair of tri shoes and oh man is there is difference. in fit and power transfer with the stiffer bottoms.  are there better things to spend $200 on? yes. without a doubt.  

Thanks for the further replies. Working on my engine is important to me, so I think I'll keep an eye out for the parts casually, but save my pennies for a trainer come late fall so I can ride in the winter.

I don't expect any speed gains from components, I'm actually looking for smoother. I test rode a bike way out of my price range, and it had 105 components. I thought it felt like butter, compared to what I wound up with, but I had a budget, and thought I could live with it. It's still liveable, but...I wouldn't mind something smoother, I guess for the enjoyability of the ride.

Someone above also mentioned a new LBS for a tune-up. It hasn't been many miles since my last tune up, so while I enjoy the service and help they've provided so far, I think I'll give another LBS a try to see if they do better. My husband also knows how to adjust the derailleur, and I'm interested in learning to do more of my own bike maintenance. Let me know if you think this is a terrible idea and if it's best left to the pros. (Doing own basic tune up.)

Okay...now to look for a fluid trainer!

Putting the engine aside and you have money burning a hole in your pocket...

I would probably go with clipless pedals first and foremost.

Then maybe a lighter set of training wheels (depending on what you have).  I got a pretty decent bike and the first thing that had to go, even though everything else was pretty solid (105/Ultegra) was the undustrial wheels.  something like 32 spoke monstrosities that were bomb proof, but HEAVEY.

Swapping out a triple for a compact crank (if you have one).  Basically same range of gearing with less weight and slightly better shifting because you only go between two rings up front instead of 3.

Aerobars (if you are looking to go aero)

fast forward seat post (again, if you are looking to go earo)

Of course, if a sadle is uncomfortable, get a new one of those earlier.

I would replace the drive train once it breaks or go with a 105 if you find it on sale or something.

Learn to adjust/maintain your bike to keep it running smoothly.

To go to a compact crank, does one need to swap both front and back or just the front?

My wife has the same bike but a year older and at one point we were looking at upgrading the components on it at some point.  It turned out to be a little more involved than I thought.

We had thought about doing a few things to upgrade it.

1) upgrade shifters and front derailleur

2) while changing the front derailleur, considered a compact double (she has a standard triple now) which would mean we would have to make sure that the derailleur would work with whatever setup we had.

3) also considered upgrading the 9-speed to a 10 speed.

4) change her wheels.  Those suckers are heavy!

The problem is that once we tallied up the cost of getting everything we wanted, it was practically the cost of replacing the bike.  So we're probably just going to replacing items as they wear down now.

I'm thinking her bike my "inherit" parts from my bike at some point ;-)