I never knew you should have a cup of water for metallics and a cup for non.
I would recommend another cup of "clean" water for diluting paint, inks, or washes on the brush.
I use old blister packs as paint palettes. Great way to recycle them.
Lighting is also key. I have a $20 adjustable lamp that can swivel in a variety of directions. Depending on what I'm painting I can angle the lamp to avoid shadows on the spot I am currently painting. I've read that daylight is the best to paint by but given that almost every person who sees your army will see it under florescent lighting, I recommend using that while you paint so it looks the same at a tournament as it does on your painting table. I have often been kind of surprised at how my army looks on the table because the lighting where I play is very different from the lighting I paint under. A lot of people also use magnifier lamps. I don't because I don't care enough to, but I can see myself using one in 10-15 years as my eyesight gets worse.
GW brushes suck as they last about five seconds before they fall apart and splay. I have found they can last a lot longer if you use brush conditioner on them, easily attainable at a good art supply store.
Speaking of art supply stores, know where a good one is and visit it. Michael's doesn't count because it sucks. If you're very knowledgeable and know exactly what you need a place like Michael's can be okay. If you need help or want to find much higher quality art supplies that will make you a better painter, I recommend Blick or Pearl Paint, dedicated art supply stores with actual artists working there who know what the hell they're doing. Going to an art supply store can be very eye opening as you can get paints, textures, mediums, flock materials, terrain making material, etc., at MUCH cheaper prices than what GW or other companies will sell the stuff to you for.
Washes and inks are your friend for getting models table ready quickly, as is dipping. There should be no reason why people have unpainted models on the table. Here's how I avoid that:
1) Figure out your color palette. Let's take my WoC for example. I wanted to go for a dark iron plate armor look like the one found in the movie Excalibur (if you play WFB and haven't seen this, you need to). This means I need lots of metallic colors. I will need darker ones for my base and lighter ones for highlighting. Having all silver based metallics will be boring, so I want to add some contrasting colors. These will be reds and blues because my army is Khorne and Tzeentch.
2) Wash wash wash: I want a really dark iron look, and when you want a dark look, starting with black primer works really well. I would then have to very subtly add layers of successively brighter metallics and greys so as to keep the black very prominent. This would be a real pain for the 100+ chaos warriors I have.
Instead, I prime them a bright silver and hit them with gobs of Badab Black wash (now called Nuln Oil because GW sucks, I mean what the hell is a Nuln Oil anyway? At least Badab Black had "black" in the title so you know what color it is). I now have a model that is instantly shaded from grey silver, to very dark silver, to black in the crevasses. I can now highlight and add details. The magic of this technique is that it takes five seconds and your army will not look like crap if you just put it on the table like that. Will it look Gold Demon awesome? No, but it will be passable. You can now take your time adding more paint and finishing every model, but if you want to play some games in between, you won't have brightly primed or bare plastic crap on the table.
3) You can do this with almost any kind of miniature as long as you follow step one well. It does work best on models with little to no skin showing like knights and space marines. My police Yu Jing? Primed white with Asurmen blue wash. They now look like shaded, blue based cops and I can add details in between games. My cowboys from Black Water Gulch? Primed white, black wash so they now have their details highlighted. Because they show a lot of skin, I have to actually put some detail paint on to make them look like they're not ghosts. Asurmen Blue on the pants, Devlin Mud on the shirts and spaghetti western coats and they now looks like they have pale skin and clothing. Add flesh tones in between games, paint the guns silver with a Badab Black wash, and poof done.
Now again, this method is not going to win you any painting prizes (although this is what my army looked like at Crossroads where I got a better painting score than Dave which shocked the hell out of me), and I have received many obnoxious comments about how my armies lack detail. It does look 1000 times better than bare plastic or white primer, however, and there's unfortunately a lot of that down at BG. It also lets your army sort of look painted while you paint it as opposed to look half painted or unpainted.
It will also probably not produce an end result as good as GW style highlighting or building up layers of color even when you add loads of detail to your models. But for someone like me who just doesn't have the patience to get my armies to that standard, it will give your army a solid "table" quality paint job with a lot less hassle.