I just got some black guard of barad-dur but I am not sure what paints I need, what order to apply them in and what techniques to use.

Depends on a few things. Do you want GW color scheme and what is your skill level?

base coat abaddon black.
Armor
pick out with LeadBelcher, wash with Skrag brown, wash with 50/50 rhinox and abaddon black. Then adjust with leadbelcher again, then highlight where needed with mithril/lead mix 50/50 to suit.

Skin
Use your favorite skin colors for Mordor Uruks. Cool colors work well as a contrast color if you go warm on the rest, or use a warm color to compliment the scheme as you seem fit.

Cloth & shield
layer up by either using Eshrin grey or you can use Steel legion Drab for a more warmer tone (harmony with reds too).

either of the above choices mix at 50/50 ratio's with Abaddon black for each layer (adding 50% more of the lighter color to the mix each time).

once you feel you have defined black as your shadow color (you can fix your shade layers at anytime or wash back if needed) then you can highlight the highest points by adding a lighter color to the mix, Ushabti bone, XV-88, Dawnstone grey all can work for this (warm or cold colors again) at 50% or less to lighten your final mix to suit.

RED
Assuming you want the red colors. pick out with Khorne red. Wash with Doombul or rhinox as you need. adjust with khorne, add Troll Slayer orange to Khorne a little at a time for layers and highlights. You can add white or bone colors near the end for the peek highlights but be careful you don't go too pink on it.

Best I can slap together for my scheme. I did paint 24 of them.

_________________
http://www.sithious.webs.com

Black for the clothes. Wash clothes with Biel Tan Green. Paint the armour, weapons and shield Leadbelcher. Wash armour, weapons and shield with nuln oil. Drybrush armour, weapons and shield with leadbelcher again. Paint the flaming eye with memphiston or khorne red. Highlight with wild rider red if you want. Skin can be bugmans glow with an agrax earthshade wash or a castellan green and biel tan green wash. For the bases try painting stormvermin fur, drybrush with either dawnstown grey or underhive ash. The base rim can be either steel legion drab or dawnstown grey. This is just the way I would paint it

I want to get them like how they are shown in the pictures on GW website. What you have both said is really helpful and I am going out soon to get those paints I don't have, but for the large part of the shield, do I leave it just abbadon black to get it like they pictures or do I do it like the rest of the armour and just wash it with extra nuln oil to make it darker?

thanks

Personally I would paint it similar to the armour and weapons but instead of drybrushing it leadbelcher after maybe just wash it again with nuln oil to make it darker.

If you are meaning the black backdrop of the shield. Paint it as you would the cloth but with flat area's you should not highlight too much. A first tier/layer blend at the top or where the light hits it most (depending on the angle of the shield per model) is enough, then your second layer highlight should only go along the upper rim (again look at how the shield is angled to determine what is top).

Keep in mind that the shields tend to pop off fairly easy, if you can pin the shield secure.

_________________
http://www.sithious.webs.com