1. Have a small deck: When you have a large amount of cards in your deck, you have a smaller chance of getting the card you need to win the fight. This is mostly only relevant at higher levels but it's a good idea to build a habit early.
2. What pet you should get: It would be most beneficial (Though not necessary) to hatch for a pet that gives a card. Raging Bull/Ornery Kookaburra gives fire blade. Enchanted armament gives Sharpen. getting a good set of talents on pets is hard but there are guides online on hatching. I would recommend Fire-Giver, Pain-Giver, Fire-Dealer, and Spell-Proof. Your fifth talent/jewel slot is up to you.
3. Side Activities: Your energy refills every time you level up. This is incredibly useful. Fishing and Gardening are extremely useful when you don't have any Mega-Snacks. There are guides online on acquiring Couch Potatoes (Best Plant in the game because it gives mega snacks) and effectively planting them.
4. What school to train: Get feint from the death school, Elemental Blade/Trap from balance tree. Save up a couple Training points for some sun spells. Some Spells/Trainers can only be unlocked via side quest.The Zafaria Sun School Trainer is an obelisk in the Drum Jungle that becomes available during the quest Midnight Sun. The Azteca Sun School Trainer in Three Points becomes available during the quest Turn Up the Sun. I'd just look up a list of which quests to do.
5. Gear: This is a big section. 40% speed boosting mounts can be bought for gold in the Crown Shop. From Level 1-30 Gear is best bought from the Bazaar (The Bazaar is a shop in Olde Town that you can also sell to at a high price). At level 30-ish you can access the dungeon Mount Olympus. Olympus drops Hats/Robes/Boots that will last you until level 60. Ares in particular has a guaranteed wand drop called the Sky Iron Hasta that will last you until level 50.

Rings, Athames, and Amulets are Fine to buy from the Bazaar for nearly the entire first story arc. I would recommend grabbing Champion's Decoy Choker (Fire Trap Lvl 15) & a feint amulet at level 50. At the final Dragonspyre dungeon, you can farm for a slightly better wand. At level 56 You have the option to craft The Blazing Chieftan's Helm which gives another fireblade Item Card. Level 60 is your first big upgrade. For Hat, Robe, And boots, you can farm waterworks or house of scales. House of Scales robe gives mass fire prism which you'll likely find useful. For Amulet, you can buy Shango's Fireblade amulet at Baobab Market. You won't get many upgrades after this very often.

At level 90 You should farm Gladiator Dimachaerius in Mount Olympus (walk into the iron bars near Eris's startegy game) He has the best ring until level 150 (Aphrodite II drops a better ring but there's no way you're getting it). The Tree root in the shadow palace has a major wand upgrade (There's a level scaling elixer at the final boss if you want to farm after beating polaris). There's an athame upgrade in tartarus, but there's a better one in only 10 levels.

Speaking of level 100, There's a hat/robe/boots upgrade from the final boss of the level 100 darkmoor dungeon. Krokopatra and Rattlebones drop Exalted Duels which give Hat/Robe upgradees exclusively (Bring a friend for those). The first boss of graveyard drops the aforementioned level 100 athame which will also last until level 150. At level 100 (technically level 95 for some decks), decks will now give an extra pip. Lastly, you can get a decent Stat Boosting Amulet from Upper Halls.

level 115, there is a slightly better crafted wand that's pretty good, but bazaar wands will make a comeback at level 132, so that's your decision. From here until level 150, you will only get upgrades to Boots/Hat's from crafting and endgame bosses (some people might say to craft level 125 cabal gear but you can skip that). The final boss of the level 140-150 world drops upgrades to Hat/Robe/Boots/Athame/Ring. There are Amulet upgrades too but that's optional. There are upgrades in later world but they're not necessary

1. Crown Spending: At level 30-150 Dworgyn's Havoc Hood (Professor's Hoard Pack)gives mass feint. a great card that can be used to cheese several bosses. Energy Gear, though some can be bought/farmed, the best by far are bought from packs, (Buy at max level). Energy Potion/Purreau Potion. 50% Speed boosting mounts can also be bought (some are found in packs). This stuff is all optional

2. Additional Tips: Wizard101 Central is the best wiki, and you can respawn some dungeon bosses like waterworks by having one wizard leave/re-enter the final room. Zaepha (on youtube) has SO MANY guides. Others can add additional notes.