Are you getting ready for your first domestic or international air travel. You should be careful about a few things:
1. Relax, nothing to panic or be concerned of. You'll enjoy the flight.
2. Before leaving for the airport, ensure that you have the Must Have items. These include flight ticket (printed / digital), Govt ID proof (some airports don't accept PAN card as a valid ID), Money, other stuff critical for the purpose of your travel (documents, etc).
Everything else is Should Have, don't panic if you forgot to bring along the other items.
3. Travel light. Also distribute your luggage smartly across cabin and check-in bags. Consider the weight restriction put by the airline. You'll be charged for extra luggage weight.
4. Pack all Must Have stuff in your cabin bag so that they are always handy with you. Also stuff that makes you comfortable should be in the cabin bag - headphones, chargers, books, etc. Everything else goes in the check-in bag.
5. Reach the airport about 2 hours before the flight time. This being the first flight, you might need time to figure out process, explore the airport. Also, early check-in gives you the opportunity to select the desired seat.
6. Select the window seat, most preferred for most fliers.
7. Eat as usual, before leaving home, at the airport, during the flight - get your food or buy it - anytime. Don't remain empty tummy for a long time as this might spoil your experience. Also, keep drinking water. Cabin is kept at low humidity and your body loses water faster.
8. You might/might not experience pain in your ears due to air pressure change. That's normal. Ask for cotton or ear plugs if you feel like.
9. Feel free to call for assistance at the airport or during the flight. People are paid to help you so don't think that you should not.
10. Share your first flight experience here as comment and keep sharing your own experiences with others you might need it!