So... I'm a relatively new player to Elder Scrolls Online, but here are my tips anyway. Hey, keep in mind, I'm Level 17, in a level 14 max area. I must be doing something right! I'm a beast!
1. Don't rush through Cold Harbour. Check all the containers, kill lots of beasties. Explore every nook and cranny for chests. And you will come out of there geared up, and with crafting mats to use and break.
2. Might be worth it to subscribe to ESO Plus, even if only for just one month. It did include 5 xp scrolls, and I used them all up once I reached Stonefalls.
3. Do all the quests. Check google to see if you have done them all, especially the start islands. I know on Bleackrock there is a quest I almost miss. But I found it eventually!
4. Crafting, do it. Do all of it. Blacksmith, woodworker, clothier, provisioning, alchemy, enchantments. You get XP gain for crafting! Mainly, break all your excess armour and weapons, if it's not equipped, break it. You even get xp for breaking. Don't sell that stuff, break it! Well, first check if you can "Research" anything, then break the excess. You can even pick up crafting quests, for more XP!
5. Have a little daily logging on, or logging off routine: Train horse (for making your mount faster, sturdier or add more bag slots). Think for horse training, the wait time between training is 6 hours? Check Blacksmith, Clothier & Woodworking for new items to Research. Because you can only "Research" one item for each every 20 hours.
6. When choosing new abilities, keep it to a minimum. You only have a few ability quick slots anyway. Instead of selecting another new "ability", put points into passives instead. Or morph the abilities you already have. Pay attention to the descriptive text too, some of those passives might have prerequisites to be effective. When I have a chance for a morph or passive, I tend to pick the ones that give health back while in combat. I want my Nord to be really tough. Also take note, you can put points into a lot of areas, not just your combat ones. There's the Racial, the armour, the crafting, the guilds, etc! Check those, good stuff to be found there!
7. Find a Mundas Stone, you get a permanent effect from those. I've chosen The Lady, which I found in Stonefalls. "Increases physical resistance by 1280".
8. Check all the bookcases, some of them give you bonuses.
9. Join the Fighters guild and the Mages Guild (and other guilds too if able). Even if you choose not to follow through, they add more quests when you are starting out, nice lot of XP gain, and helps you out by making you explore the map and find other stuff.
10. Be a sneaky thief. Umm... Steath around a lot. But chests that are locked, you don't have to struggle with the "lockpicks", if you have lockpicks and you hate the lockpicking in this game the way I do, you can just keep selecting "Force Lock". It works!