1. One of the easiest ways to earn a top-tier Pokemon is to write a story for Magikarp. Requiring only 3,000 characters, a Magikarp in one of the easiest Pokemon to write for, and with only seven battles, can evolve into Gyarados, a powerful creature indeed.
2. Battle early and battle often! Each battle in the URPG will reward you for participating, no matter if you won or lost. Losing may only reward $500, but those tiny amounts slowly add up. Many refs would be happy to run a battle for you and if they're busy, simply ask another. After all, they earn money too for reffing.
3. Form rivalries with other members who have started around the same time as you. Not only does this give you someone to battle with when they're on, but most likely they will also be at the same skill level as you, making the duels a challenge in and of itself!
4. Don't pick a Pokemon that is available in the Pokemart as a starter. Story only Pokemon are, for the most part, better than a Pokemon obtainable from the Mart.
5. When you're in a battle, and you're not certain of something, for instance how much damage an attack will do or whether something works or not, never just guess and hope for the best. Ask the ref, they'll be glad to answer, even if it's something stupid.
6. When you train your first Pokémon, don't try to fight older, experienced members. Try to fight people that have newly-bought-or-caught basic Pokémon like you, so you'll have more chances of winning, and getting more money.
7. If you have AIM, go to the Reffing Encyclopedia and get the screen names of all the active refs so you'll have a big list of them on hand and won't keep bothering the same ones over and over again.
8. Begin to write early and it'll be easier lately.
9. Your second Pokémon should try to counter what your first Pokémon can't fight.
10. Ask older and more experienced members how things work. Sometimes you'll find exceptionally nice people who don't mind helping you out and teaching you a bit.
11. Be nice, be yourself, make friends. Remember that the other members are still real people too. If you make friends, you'll have more fun, and will probably have more support and go further.
12. Don't teach your Pokemon any TM just because they can know it and it seems cool at the time. Do your homework and figure out which TMs can benefit your Pokemon the most. Buy the most important ones first (like TM Calm Mind and Shadow Ball for Espeon) then, when you have more money, you can buy other TMs. Don't be afraid to ask more experienced members for advice as to which you should buy.
13. READ this thread (BMG | PWN)
before you even attempt to post a story. There are certain expectations for URPG stories that will differ from other stories you might be accustomed to writing. Don't get angry when graders criticize you, either. Take their advice, read it, and grow from it. They're here for your benefit.
14. Every Pokemon you have can be used whether it's just for battling, contests or extra-curricular activities. And if you want to use a Pokemon everyone says is useless, that's your choice. I say prove them wrong.
15. To get stronger quickly, only get a few mons and concentrate your money on giving them vital moves such as set-up moves, or moves that give you essential coverage, such as Ice Punch on Metagross. After you start winning a few battles, you can be more laissez-faire about spending and go into niche moves that may turn the tide of a battle (Jolteon's Shadow Ball).