Greetings, and I'm starting to feel repetitious throughout my postings by now. =p
A few general tips I'd give you: Orks have crap leadership. When you're using Orks in such a way that you're not exploiting their "Mob Rule" special ability, they're wasted. If I were to play your army, the first thing I'd try doing is making your Lootas and attached meks run off the table, followed by your Tankbustas and Nobs.
Your base leadership is 7, and 7 is also the magical number of an average dice roll. If I kill 2 Nobs, or 2 Tankbustas you're going to take a leadership test, and you've got a 6+ armour save going for you to make saves against.
With that said, there are a couple of principles that sort of guide orky goodness: Orks can do ANYTHING as good as any other army can. However, Orks cannot do it all at once. You have to pick an objective for a particular army build and focus around that. Either foot-slogging, or mechanized, or shooty, or sneaky, but you can't have a bit of all of it effectively.
Another note to make here: An ork boy with a shoota (6 points) is one of the most cost-effective, if not THE most cost-effective units in all of Warhammer
40k. Also to note: Ork powerklaws are great anti-tank.
With that said, pick an element of what I said above, and try focusing an army list around it. Your units should always be maximum size where possible. 15 Lootas, or 30 Boyz, or 5 Deffkoptas; the strength of Orks is in their numerical superiority, not their ability to outshoot or outfight another unit one on one. Your 30 Boyz are going to mess up a squad of space marines. Or a squad of terminators. You're not going to go model for model; you're going to take heavy casualties, but that hidden powerklaw is going to mess some junk up. And given that you can lose 4-5 models for every casualty you inflict (against terminators for example) and still stay ahead in point calculation, you'll do well for yourself.
So, my advice: Drop the big shootas, the armour plates, the reinforced ram, the Deffkoptas, and the Lootas, and probably the tankbustas too. If you're going to have 60-90 boyz foot-slogging out there anyway, then capitalize on their foot slogging and get 90-120 of them out there doing it. Might want to even consider adding 20 or so Gretchin to the front line, stretch them across your lines, and give all your Ork boyz a free 4+ cover save as they advance.
If you're going to foot-slog across the board, take shoota boyz. Thats a LOT OF DAKKA when you get within 18", which will be turn 2, or turn 3 at the latest; and you'll have a pretty good survival rate if you've got gretchin giving all your orks 4+ saves. And gretchin are 3 points apiece.
Nobs have the ability to be ridiculously strong - you can literally take a unit of 10 independent characters in regard to wound allocation. Stick a painboy in there and they all get 4+ feel no pain. Given them 'Eavy Armour and now they have 4+ armour saves, and 4+ Feel No Pain. Equip them differently, and you can spread wounds around. Here's a common list for me of 10 Nobs:
1. Painboy
2. Waaugh Banner
3. Bosspole
4. Powerklaw
5. Powerklaw / Ammo Runt
6. Big Choppa
7. Big Choppa / Ammo Runt
8. Skorcha
9. Ammo Runt
10. Normal Nob
Now, if you take 4 wounds to the squad, you allocate them how you see fit. Point to a nob and roll a wound, then a feel no pain. Etc.

Having a Waaugh! Banner means
WS 5, so in close combat, you're generally going to need 3s instead of 4s now. Its worth it for 15 points. As for the trukk: Either give everyone a trukk, or lose the trukk entirely. With a single trukk, you present a target for anti-tank, and with only one, it WILL be gone turn 1 in every game, and you'll be wishing you had spent those 35+ points elsewhere. A common tactic for me:
Nobs+Ghazghkull in trukk
3-4 squads of trukk boyz
Mad Dok Grotsnik + 19 'Ard Boyz inside a battlewagon (they all have 4+ feel no pain because of Mad Dok)
If you're going to foot slog it, honestly...I'd trade out the Mek with the
KFF for Mad Dok. a 5+ statistically doesn't give you much, and Mad Dok confers Feel No Pain on his unit. Try this on for size and see how it fits: Mad Dok Grotsnik attached to 30 Boyz (one with a powerklaw) who are also your 'Ard Boyz mob. This huge unit now has a 4+ armour save, a 4+ Feel no Pain, and a 4+ cover save from your screening gretchin.
Alternatively, make THIS your screening unit. Have these Orks screen and give cover saves to the rest of your Orks marching up behind them. Your enemy can either try concentrating fire on this unit to take them down (and with Mad Dok you're permanently fearless), or they can shoot at the rest of your army who is getting 4+ cover saves. Either way, the Orkish horde is going to annihilate your enemy. I don't want to ramble on too long, so try it and run with it.