The most popular way to make your kit look it's best is to paint it's detail lines. Some people think kits look best with out them, others think they look best when done in heavy black. The popular consensus however is that you should line with a color and darkness relating to the plastic you're working on.

For example, when lining on white use a light gray. For medium colors try a darker gray, and dark or somethings vibrant colors use a black. If you're lining with paint try to mix in portions of the base color for a subtle effect.

Remember to try different things and go with what you think looks best.

Lead Pencil

The easiest way to line is with a lead pencil. Easy to use and fairly easy to clean up. Lots of people use 'em and like 'em. Personally, I'm not a huge fan. It's very easy to smudge when handling a piece. It also has an odd, almost metalic sheen, that bugs me for no good reason. If you're going to use a pencil it's imperative that you apply a top coat after to protect the lines.

Gundam Markers

These babies have been crafted by Bandai to both take more of your money (they're inexpensive, really) and help your Gundam look sexy. I'm not to sure of what sort of ink/paint they use, I heard acrylic, but I can't read Japanese. Gundam markers are just as easy to use as a pencil. When they're still wet they clean up easy with paper towels. When dry you can remove excess with light sandpaper or an eraser.

The two sets I have (seen above mixed up between their original packages) are from the Real Touch line. I'm not sure what makes them special but they work great. One end is a normal tip and the other is fine.

There are also fine tip Gundam makers out there feature a really small, .25 mm, tip. For whatever reason these always give me trouble. The tip doesn't hold up too well over flat paints and never seems to apply as much as the Real Touch ones.

Alternative Markers

When it comes to doing detail lines Sakura makes a fantastic alternative to Gundam Markers. Their line of Pigma Micron pens are available in ton of colors and sizes. The best part is that you can find them at most chain craft stores like Michael's. I use them all the time.

The only issue, there's always one, is that there's no gray in their lineup. I've tried a couple offerings from Copic but they were either too light or had an blueish tint. Thus my search for a replacement continues.

For those interested, here's a tip comparison...

From top to bottom, .07mm mechanical pencil, BIC ballpoint pent (courtesy Holiday Inn), fine tipped end then not so fine tipped end of the Real Touch Gundam Marker line.

Eraser

Great for removing excess pencil and Gundam marker. Get a smudge free one if you can.

Paper Towels

Paper towels are good to have on hand when working with the Real Touch makers or paint. They make a fine job of cleaning up excess while it's still wet.

In addition to paper towels you're going to need a bit more on hand if you're planning to line with paint.

Paint & Thinner

This should go without saying. A small jar of paint and some appropriate thinner (aka get the right kind for the type of paint).

Toothpicks

While one might not expect it, toothpicks are pretty important. When hobby paint sits on the shelf for a while it likes to congeal at the bottom of the jar. Shaking helps but never enough to break up the bottom mass. Thankfully we have toothpicks to come in and save the day by string things up.

They're also useful when poring paint from one jar to another. If you poor the paint onto a toothpick it will help as a guide lessening the chance of missing your target.

Mixing Container

A jar or little dish where you can mix the paint and thinning agent. I usually use an old, like color, paint jar.

Fine Tipped Brush

When applying the paint it's best to use a strong, fine tipped brush. The more precise the point the better.

Fine Grit Sandpaper

When working on plastic fine grit sandpaper will make quick work of any excess. The finer the grit the better, I recommend 600 and higher.