Alright, so you want to 100% Need for Speed Heat. 

You'll need REP 50 to unlock the final missions from Dex. Don't stress too much about anything else, just play at your own pace and enjoy the game. Try to grab collectibles and smash cops along the way so you have less cleanup later. Also, consider saving up $1.2 million for the Koenigsegg Regera.

A quick note on that car: I mention it for some specific achievements and collectibles, but you don't absolutely need it. You can probably pull off the same things with other supercars that have Ultimate or Ultimate+ parts. That said, getting those parts means grinding a bunch of Heat 3 and Heat 5 races. Saving up the money is way faster, especially since you can just accumulate it during your normal playthrough.

Pretty self explanatory. There's a great map linked in the "Collectibles & Activities" section below that shows you where everything is.

Finish off whatever achievements you're still missing. You'll also need to complete 25 online races. Hopefully you can join a Crew that's already max level, otherwise leveling one yourself is a serious grind.

These are part of the story and impossible to miss. You need to complete all character missions and hit REP level 50 for the final few missions with Dex.

Pick your first ride

Complete Chapter 1

Complete Chapter 2

Complete Chapter 3

Complete Chapter 4

Complete the Drift driving story

Complete the Off road driving story

Complete the story mission

Reach REP Level 2

Reach REP Level 50

Win a race in a vehicle with an engine swap

You'll need to get all billboards, graffiti, and flamingos, plus 3 star every long jump, drift zone, and speed trap. There's a great interactive map linked below where you can see all points of interes, you can right click to hide completed locations.

You can collect things along the way to make it easier later, but some speed traps and jumps require you to have one of the supercars or the Koenigsegg Regera, which unlocks at REP level 50.

Get all collectibles and 3 stars on all activities

Get a 3 star rating on all activities in the game

Smash your way through all the billboards

Collect all street art

Collect all the flamingos

Complete all speed traps

Complete all long jumps

Some jumps are on dirt roads. For those, spec your vehicle for off road/race.

Complete all drift zones

Supercars may not be the best choice for these. I struggled with some drifts in the Koenigsegg Regera. Instead, get a car that leans toward drift straight from the dealership, then equip additional drift/road parts. Also, spec your car for off road when doing off road drift zones. Some of the best cars for this are the Mazda RX-7, Nissan 350Z, any Chevrolet Corvette, or the SRT Viper GTS. You can find more info in this great guide.

Change the text on the license plate

Customize a vehicle with a wrap

Win a race with parts equipped in both auxiliary part slots

Win a race in a vehicle with tuned exhaust sound

Win a race with all vehicle effects slots equipped

These include 6 effects: Nitrous Color, Backfire, Tire Smoke, Underglow, Air Suspension, and Horn.

Parts that affect handling are Suspension, Tires, and Differential. Change these to max out all 4 types of handling.

Win a race with handling parts for maximum drift equipped

Win a race with handling parts for maximum off road traction equipped

Win a race with handling parts for maximum road traction equipped

Win a race with handling parts for maximum race equipped

Repair critical damage at a gas station at night

Do this at night when you're in the last section of your damage bar.

Escape 100 cop chases

Take down 100 cop vehicles

Cop escapes will be pretty easy, but this one takes a bit longer. Just smash into cops whenever you can, especially when they first start chasing you. Consider getting the "Damage Increase" passive auxiliary part to do more damage. Taking most ramp jumps will also crash some cops chasing you. It's good to farm this while going for "Cashing In" below.

Win a High Heat 5 race and return to the garage safely

Earn and bank 1,000,000 REP during one night

Not as hard as it sounds. You can switch to easy mode to make it easier. Start by doing any races to get to a Heat 3 race, finish that, then get to a Heat 5 race and finish that too. Now with Heat at 5, go to this area in Downtown Palm City. 3 star the 2 speed traps and repeat until you hit 1 million REP. The jump is also a good spot to farm crashing cop vehicles for "Eleven - Fifty Six."

Complete your first Daily Challenge

Go from last to first place during the final lap of a race and win

Easiest once you have a supercar. Put the difficulty on easy and pick one of the first day circuit races that look pretty short. Change the race score to 120. A good race for this is called "Tornado" at Downtown Palm City.

Win the Discovery Event

The Discovery race unlocks once you reach REP level 50. It's a night race with a 400+ gear score rating that shows up somewhere on the map. It takes about 9 minutes to finish. Best done with one of the supercars or the Koenigsegg Regera. You can get this in tandem with "I Said Right Now!"

Win a race with a car at 400+ Performance Rating

Hit 240 mph using any car

That's 386 km/h. Best done with a supercar or the Koenigsegg Regera. Find the straightest line you can and get to top speed. Equip a 1 x 12LB Elite Nitrous to boost you to the required speed.

Beat your first Crew Time Trial

Crew Time Trial races have a stopwatch icon and are pretty easy to complete.

Reach max Crew Level with your Crew

You need to get to Crew level 50. It's incredibly grindy to do by yourself. Best thing is to join a Crew that's already level 50. You can ask or find somebody offering over on the game's discussions page.

Complete 5 events online with other players

Complete 25 events online with other players

Some of the fastest races to do these on: