(In alphabetical order)
1) Control your different types of Pokeballs and Razz Berries
Try to save your Razz Berries for rarer Pokemon you have never seen before, or Pokemon with high CP. Use a Poke Ball for Pokemon which are under 200 CP, Great Ball for Pokemon which are 200-500 and Ultra Ball for those which are 500 CP. Those without the use of Razz Berries. That way you will save your Pokeballs and Razz Berries, which means more EXP for you when the opportunity comes.
2) Don’t ignore Pidgeys
Pidgey is a very common Pokemon, and every time you encounter it, you might be like Not again this. But it’s actually the best Pokemon to catch because it gets evolved very quickly (it needs only 12 Pidgey Candy), which means you can gain much EXP quickly, if you have many Pidgeys caught.
3) Don’t try to go for the Stage Three Evolution
I mean for example if you have a Machop, try to evolve it to Machoke and then at Machamp but ONLY ONCE. Remember to evolve a Machop with lots of CP, to the point it will be Machamp, so you can use it for battles later. Don’t try to do this with the other Machops because it will be a waste of Machop Candy, and also you will gain less EXP. Evolve it till it becomes Machoke only.
4) Save your Pokeballs
If in case you are in lack of Pokeballs and you are on the road, then avoid catching any Pokemon (unless you encounter some Pokemon you never had before, so give it a try if you do) but try to find as many Pokestops as possible to gain more Pokeballs and use them at some better area (see #5 for example). You will miss the opportunity to gain lots of EXP, if you have all your Pokeballs wasted.
5) Sit at a café with lots of Pokestops
And try to find a good spot, for example one where you will have four Pokestops around you. Usually such areas draw lots of Pokemon and if you have many Pokestops around you, you won’t be in lack of Pokeballs soon. That way you will save lots of your energy, since you don’t have to wander around to chase Pokemon, and gain lots of EXP too.
6) Use Incense on the right time and at the right spot.
Use it in an area with many Pokemon available, and never on some isolated area. Also it would be even better to use it when there is a Pokemon you have never encountered before in this area, so be careful about when you will use them.
7) Use the Lucky Eggs by the time you have many Pokemon which are about to be evolved.
You get 1000 EXP for each Pokemon evolved, and 2000 if you have never had this Pokemon before. So if you evolve thirty Pokemon, you will gain at least 30000 EXP and maybe some more.