Hopefully this thread will help save ALL of us some time and frustration, there are WAY too many questions like "my car won't start, what do I do?"
The first thing you should do is to make sure that ALL of us know what vehicle you are talking about. Some of us get our jollies by offering tips related to Peterbuilts, Escalades, Barbie Jeeps etc. and the transmission type makes a difference as well as what year/make/model. So make yourself a signature line that tells us, they only seem to show up when you are logged in, so only the members will see your signature, you may as well put the info in your first post, but if we are trying to help you make it as easy as possible for us to find the important information.
Also, just because it won't start does NOT mean it needs a starter! We need to know if it cranks, clicks, smokes, or does nothing when you turn the key.
I made the video attached below, (first time trying to attach a video so I don't know if it will work) showing some basic troubleshooting when my wife's Honda CRV quit running last week, so here are some pointers.

#1 Get all of the information you can, I was 800 miles away when I got the call that it died, so I asked all the stupid questions first, does it have fuel? did you hear funny noises? did it do anything else funny in the last few days? Does it crank energetically? What I got was, Yes it has fuel, yes it cranks, a few days ago it didn't want to start but did, it was running and as she drove down her long driveway it just shut off and would not even try to fire. If you are asking for help on forums make sure to tell us the WHOLE story!

#2 Do some quick tests to determine what direction you need to go with the troubleshooting, do not jump to conclusions! Check fuses first, they are easy. Make sure there is power at both sides of the Ignition and fuel pump fuses (check your wiring diagram if there is any doubt where they get power, or use the fuse panel lid/door sticker etc.), give it something to burn (a small shot of starting fluid) and see if it fires. No fire means it is likely you have no spark, fire means it is not getting fuel either because the pump is not supplying pressure/volume or the engine control module is not energizing the injectors. If you have done ANY testing let us know what you have done and what DEFINATIVE results you have. Nothing like "it gets spark and the fuel pump fuse it good, so it needs a pump". TEST for POWER and GROUND at the fuel pump, GIVE it power and ground and see if it works.

#3 After finding out which way your troubleshooting needs to go research the wiring diagrams for your vehicle, look for you-tube videos for component testing etc. My testing quickly led me to checking the coil and I found a video that was super helpful and with 10 minutes TOTAL of troubleshooting I found that there was no spark and that the coil was bad. 10 minutes of repair time after a trip to the parts store and all was fixed. I won't get too deep with the wiring or the final testing or repair because it is all Honda specific.

#4 When you find out what the issue was and get it running again post your results including any tips/tricks you came across that will help others in the future, there is nothing worse than telling a joke and keeping the punch line a secret!

Somebody let me know if the video works, if not give me some tips on how to attach one.
Thanks, I hope this helps, I know if someone had told me all of this 30 years ago I would have gotten much better at diagnostics much faster and saved a lot of money and time.