What was the first thing you upgraded on your bike?
 

I bought puncture proof tires for my Specialized Allez

I didn't need any upgrades.

then what was the first thing you bought for your bike?

Rack and lights.

Wheels.

I have an old bike where everything has been upgraded but the frame. It's an old Waterford built with 8 speed Ultegra. The first upgrade was D/A 9 speed. Next a Thompson seatpost. Then a new saddle, followed by bars. Then a new CF threadless fork and headset. Finally Kysrium wheels.

Wouldn't consider it an 'upgrade'...more of a necessity, usually change the saddle (comfort), cassette (gearing I need/prefer), and brake pads (Koolstop salmon)...and maybe tires if I don't like the OEM ones after a week or 2. Add lights, seat bag, and computer and maybe a rear rack depending on the bike's projected use and the usual u-locks.

The basics upgrades that I first do to all my bikes are lights, mirror, saddle, pedals, and chain. Depending on what type of weather the bike will be ridden in or use it may do, determines what other upgrades I will make.

99.9% of the time is a new-cruiser bike style-saddle that is rather wide in the rear with 2 springs. Very little padding, and supportive of my own muscular and skeletal structures.

The first thing I changed was the rear tire, because my first bike had a coaster brake.

leather saddle to replace the gross vinyl one

Seat. I am attached to my ass.

pedals....when you buy a cheapo $2000 road bike, they don't include the floor mats or pedals

Saddle, then pedals & shoes.

The engine ;)

I've been buying off craigslist so I may not be upgrading so much as replacing with new parts. First to go is the saddle, I must have a comfy saddle. I next replace the brake pads, then check cables. New tires are a must! I'm not a mechanic so any work on the drivetrain will be handled by the LBS. All my bikes have their own headlight and tail blinkie. The engine is constantly being improved upon.
Ernest

Getting it out of storage - grease, cables, housing, rubber. Then came the seat. Terry saddles are great!

Tires. Always the first thing to go.

In terms of changing the original components, I replaced the stock plastic pedals with MKS pedals. Next I'm replacing the original grips on the flat bar to Ergon grips with bar-ends, suspension seatpost to rigid, and quick release seatpost clamp to non quick release.

All Terrain Tires, it came with Racing Tires

Tires. Rim tape and tubes. And the wheels. Cranks, bottom bracket, pedals, chainring, chainring bolts, chain... Fork, brake, brake lever, handlebars, bar wrap, stem, headset... Saddle, seatpost, and bottle cage.

All at once.

(I was upgrading from not having any of those things.)

After the lights, cycle computer, and saddle pack, my bike was pretty much the way I wanted it. After a year the San Marco Ponza saddle broke, and I replaced it with a Fizik Airone. Then got some SPD pedals and shoes to replace the toe clips. I love the power I get uphills now. I've just recently replaced the 700x28 tires with some 700x23 Vredestein tires. They feel great.

Trek 7500 Hybrid:

If a computer is considered an upgrade, that's what I did first!

Then came bar ends so I could alter hand positions, mirror. That's the way things sat for a couple of years, though went through a couple of mirrors and different computers.

This year I put on clipless pedals w/appropriate shoes. Big difference! Upgrade to a Garmin 305, so I'm probably "maxed out" in that department.

Next year it's a whole new bike! Starting to look around for a road cycle now . . .

Constant effort to upgrade the rider! That's not so easy any more . . .

1. Saddle
2. Saddle
3. Saddle
4. Saddle
5. Saddle

It took a while to find one that worked for me.

pedals then wheels and tires.