If you are using Wyeast, you should smack the pack a day or two prior to brew day, to give the yeast time to wake up. The package should swell from CO2 production, indicating that it is alive and ready to go.
With Wyeast packs like that, if they swell up within 24 hours, I usually don't make a starter. But if it seems sluggish, or if using White Labs yeast, then I would usually be an advocate to making a yeast starter...
There are instructions in books and online for how to make a yeast starter. It is really just a small batch of wort that, once again, you make a day or two in advance, to give the yeast a chance to wake up and begin to multiply.
Personally I am a small batch brewer of 2 gallons or less. In this case, I don't need to make a starter, but it's still never a bad idea. If brewing 5 gallons, I would make a starter as detailed above.
If you need any advice on which strains are favorites based on the style of beer that you are trying to brew, let us know -- homebrewers have lots of opinions on that topic!