I reckon the first thing you should do is read back up on the
official rulebook to refresh your memory of the rules. If you read the Appendices, you will also be able to learn the new mechanics that are around in this format. Once you've done that, and since you have no money, you could look at playing the game on an emulator such as the free
official PTCGO emulator. This should put those rules into practice so you feel confident. Once/if you obtain money, you can look at buying a theme deck or other prepackaged deck. I would recommend one of the Battle Arena Decks as they contain more powerful cards than your typical theme deck, and are especially helpful if you are looking at becoming more competitive again.