Some things I've picked up along the way:
For saving mana, if you can, pull more than 1. Usually outside, if the mobs are non-casters, non-elite and have mostly basic melee attacks, I can pull 4, 5 or 6 of them at a time as long as I keep holy shield up. This means I block the vast majority of their damage AND with BoSanc I never have to worry about mana at all. This frees you up to use any seal/judgement that you want (SoV seems to be the most popular for tanks, so it's good to use it and learn how it works so you can be competent at keeping your stacks up later). Almost always if there are 2+ mobs on me I can go crazy with the mana-burning attacks and remain at full. If you are still having a bit of trouble, seal of wisdom is your friend. (this is basically for leveling only though, not for running through instances, so keep that in mind). Someone here said "oom" for a paladin tank doesn't mean out of mana, it means out of mobs. Once you have BoSanc, that is ABSOLUTELY the truth. As long as something is hitting you, and you have holy shield up, you are a little mana-generating machine.
If you're lucky enough to have two friends with you that you play with all the time, tell them precisely what you're doing before you do it. Let them know that it's ok to go to town on the mobs after you consecrate and they don't have to worry about pulling them off of you (if that is the case with you, and it likely will be). Having a group like that is a huge help. There is 1 other person I always party with and she knows what I do inside and out, which makes my job SO much easier. Because, let's face it, it's very annoying with a new person you're playing with keeps pulling the mobs off of you, cutting off your supply of mana and causing you to go running all over the place.
Teach your friend(s) WHY (not just how) you do these things. Tell them WHY you line of sight casters. Tell them WHY they need to wait until you consecrate. Cement in their minds what it is we do so that it becomes second nature to them to LET YOU do your job as the tank.
You have friends, USE 'EM. Run the lower level instances (a few levels lower than you). I find that with a competent tank (which you surely are if you are reading these pages) and careful pulling, you can run a lot 'em without a healer. I know, because I've done it. It's not as easy, certainly isn't as fast, but it IS possible. This will teach YOU so much too. It will teach you all kinds of great things about pulling and what your character can handle as well as what works best for your group that you play in. Plus, you get better loot, which equips you better or sells for more gold. So it's a win-win for everyone. You won't be able to run every instance, but you will be able to run quite a few this way.
Enchant, enchant, enchant. YES, it's expensive. But you can add SO much to your character this way. Koatanga mentioned the leg armor, PERFECT!! Even if it adds on a few stamina, take it if you can afford it, especially once you get up into your 40s and 50s, because you won't be changing armor every day (although if you're running dungeons, you won't need to anyway because you'll have higher quality gear). I guarantee you there will come a time when that extra 10 or 15 stamina will make a difference if you don't always have a healer around.
For me, tanking didn't really get fun until I got holy shield. It might be a bit of a grind and all before that, but when you get holy shield, things begin to fall into alignment and you begin to realize what you're doing. So stick with it, with every level you'll find yourself getting better and gaining a deeper understanding of the core concepts of tanking.
The 969 method is talked about pretty heavily and for good reason, but you really can't do that until much later levels. So initially, find a good rotation that works and allows you to waste as little time between skills as possible. As more skills become available, you will be able to begin to work on your final rotation. Even though you can't use it early-on, remember it, because you will need it later.
Of course keep reading the pages here, there is a huge amount of knowledge contained in these pages, even on the threads that might not look so exciting. If you want to be the best tankadin you can be, you have come to the right place.
Best of luck to you. I'm working my way to 80 too (at 71 now) so I know what you're going through. It's not easy, but it IS rewarding to be a great tank. Keep it up!
-b