Individual Values (IVs) is a point value that ALL Pokes get as soon as you catch/hatch them. The point value ranges from 0-31. Unlike EVs though, the value directly affects the particular stat. If your Steelix has a Def IV of 31, that means it has 31 extra points added to its base Def stat. So, between proper manipulation of IVs and EV breeding, you can affect a particular stat of a Poke by 94 points. That is the difference between a Lv100 Metagross having an Atk of 275 and 369, and we haven't even covered what affect you can have by giving a Poke a beneficial nature. Giving our Metagross a +Atk nature, that turns the 369 Atk stat with max IV/EVs into 405, giving a total of a 130 point difference from the first example. HUGE.
If you have Emerald, there is an easy way to manipulate the IVs of a Poke. First you get the species you want to breed and a Ditto that has the nature you want. You then proceed to breed babies until you have at least 6 Pokes of each gender (if applicable). SAVE YOUR GAME. Once that is done, you feed each one 15 Rare Candies to get them to Lv20 and then pull out your handy IV calculator (I suggest metalkid's program, but not sure if I can publish the webpage) and see what their IVs are. If any stats are maxed, notate that and continue on. Once finished, reset the game. Now you keep the Pokes with good stats and then release the others into the wild. It would be wise to also note what the Lv5 stats are for the stats that you found to be maxed at Lv20. This comes handly later on.
The next step is to determine whether or not any babies of the new generation should replace ma or pa in the Daycare Center. If any have better IVs in the targeted stats, do it. Once that is done, repeat the process with generation after generation until you get two (if applicable) parents with strong IVs.
At this point, we need to cover the most important part about breeding in Emerald. In the other games when you breed, the parents will contribute three random IV stats that will be passed on to the baby. Two from one parent and one from the other parent. The problem is that both parents can pass on the same stat, effectively only passing on two IV stats. That problem was fixed in Emerald. You are guaranteed three unique IV stats to be passed on to the baby. The next best thing is that in Emerald, all values are set once the DC Dude steps out with your egg, EXCEPT the IVs. That means you can save the game BEFORE you take the egg and then reset the game if the IVs don't end up being what you wanted them to. What you do is take the egg and hatch it. Then you compare the Lv5 stats with the Lv5 stats that you should have recorded earlier in the breeding process. If they match, you keep the egg. If they don't, you reset. You repeat this process a few times until you have a good group of super babies. Then you repeat the process of feeding them RCs and then double-checking their IVs.
Voila!! You now have baby Pokes with good IVs that you can now proceed to EV train.
