Use splashy Intro Pack and other themed pre-cons face cards, if possible.
Only include cards from sets for whom the guilds mechanically mattered: RAV, GPT, DIS, RTR, GTC, DGM, GRN, RNA
An equal number of mono-colored spells (50 per each color)
A very high, but equal number of gold spells (30 per each guild)
Draft advice
Gold cards are plentiful, and usually have a high power level for their mana value.
Therefore, prioritize color fixing highly. There are 14 color-fixers per guild, including dual lands (2 Bounces, 3 Shocks, 4 Gates) and artifacts (1 Cluestone, 1 Keyrune, 1 Locket, 2 Signets) to help you along the way.
Just like drafting DGM/GTC/RTR and RAV/GPT/DIS, you're likely going to have a three-color/three-guild deck by the end. That's intentional. Therefore, I tried to avoid parasitic mechanics (for example, Dimir's Transmute and milling sub-themes) when possible.