RE: New Player Help !
Hey KingFTW, welcome back to the Pokemon TCG! I recently returned to the game this summer.
The modified format was rotated a week or so ago and is now BLW-On, meaning that only cards from the Black & White set and onwards may be used in legal tournament play. I wouldn't suggest buying any booster packs that are from previous sets unless you wanted them for collecting purposes. I'm not sure if you can redeem older packs on the PTCGO, but if you can I would suggest that you didn't do that and only redeemed booster packs from tournament legal sets.
I'll continue with the assumption that you are more interested in playing the PTCGO than the "physical" TCG at the moment.
A couple of good sets to redeem booster packs from would be Dark Explorers and Dragons Exalted. Dark Explorers contains the majority of the staple Trainer cards that you will want to use in your deck, as well as powerful Pokemon EX cards that are being used in top tier decks at the moment. Another set to redeem booster packs from would be Dragons Exalted, the most recently released set. There are a lot of cards contained in Dragons Exalted that are being used to make competitive decks at the moment. With that said, a good idea would be to look at all of the tournament legal cards, determine what cards you would like to play with in a deck, and redeem an appropriate amount of booster packs from the sets in which those cards are contained.
In terms of deck building, I'll give you a couple of things to consider. You want to determine what strategy your deck will follow and then build your deck in a way that makes it as consistent as possible in following through with that strategy. For example, in a Darkrai/Hydreigon deck, the goal is to have DarkraiEX as your active attacker and Hydreigon on your bench. Hydreigon (Dragons Exaled 97/124) can rearrange Darkness Energy as often as it likes during your turn via its ability "Dark Trance". The main strategy of the deck is to heal your DarkraiEX with Max Potion, essentially negating your opponent's last turn while you get closer to your goal of taking six prize cards. Max Potion heals all damage off of a Pokemon but also discards all of the Energy attached to that Pokemon. Hydreigon can move the Energy off of DarkraiEX, allowing you to use Max Potion to heal the damage with no drawback, after which the Energy will be moved back onto DarkraiEX. Like I said earlier, you will want to make that strategy work as often as possible. In order to do that you will want to have an amount of each of those cards that allows for the desired consistency I run four Max Potion and a heavy Hydreigon line (including Rare Candy) to give me the best chance of making that strategy happen during every single game.
I hope this information helped you!
Feel free to PM me if you need any clarification or have other questions.
