After drafting this format a bunch of times, I think everybody agrees that the first couple picks really don't matter that much in comparison to the rest of the draft. Yes, you can get powerful cards that you'll want to play, but this set is so focused on synergy due to the flat power level that you throw away your first picks at a much higher frequency than usual.
Because of this, for the rest of Ixalan, my articles will focus on picks three through eight. While this is not necessarily where you say "okay, I'm [Insert Archetype] now," it is when you get a strong idea on what is open and where you should be.
Pack 1, Pick 4
The Picks So Far:
General Limited philosophy would push me towards taking the Siren Lookout. I already have two great blue cards, and adding a third could solidify me into blue and then I can worry about my second color being whatever is open. The reason this approach works for most current Limited formats is that each color has so many playables, so even if one of your two colors is not open, you'll still get a fine number of cards for your deck. This is not the case in Ixalan, as there are plenty of commons of each color that really only go in one deck.
So while Siren Lookout is a defensible pick, I would rather speculate on synergy or take a more powerful card in another color to leave as many options available while I figure out what my seat is supposed to be. Note that if you have a bomb in a color, you should still be leaning towards taking cards of that color because it is more worth the risk.
Wildgrowth Walker is an extremely powerful card, but I'm not going to take it here. This is largely due to an aversion to green. While I don't mind ending up in green and picking up this card to build around, I don't go out of my way to do so. Additionally, since most of the explore cards are picked highly, it is hard to maximize Wildgrowth Walker. And I don't want to fill my deck with Ixalli's Diviner to make this card work out, as I would like to be proactive and pressure my opponents.
It all comes down to the best card in the pack, which I believe is Pious Interdiction. Both W/U and W/R are great color combinations, so if one of those happens to be open, I'll have a great deck. And if white isn't open, Pious Interdiction is splashable if I need it. From this point is when the draft gets interesting.
Pack 1, Pick 6
The Picks So Far:
After getting another Siren Lookout, which happened to be the best card in the pack, I'm feeling blue is where I'm supposed to be. So at this point I will be looking at each pack to confirm that blue is flowing, and be on the lookout for what else is open to find the proper archetype. But if the next three packs have no blue cards, I am completely willing to jump ship as long as there are other good options in the packs.
If I'm taking a blue two-drop here, it's going to be Shaper Apprentice. I know some players, Ben Stark for example, prefer Shipwreck Looter to Shaper Apprentice. If you have no other Merfolk, yes the looter will be better, but I like approaching the early packs of this format with hope. I would rather take Shaper Apprentice in pack one because I can value other Merfolk slightly higher for the rest of the draft (and play it in non-green decks). Once we get to midway through packs two and three, then it'll be clear which card is better. For now I want to keep my options open to be Merfolk, and I'm taking the card with the higher ceiling.
But is Bonded Horncrest the kind of card that tells me that red is where I'm supposed to be? If I was at a table with seven clones of myself, the answer would be no. Bonded Horncrest has plummeted in my evaluation, as the downside is terrible. Any form of interaction feels like a two-for-one against this card, and it's not fast enough to justify this downside. Don't get me wrong, I'll play the card depending on my curve (and access to haste creatures), but I'm not a huge fan. Because of this, I'm going to take Shaper Apprentice. I will note that it's possible the Bonded Horncrest was a signal based on where the rest of my pod may value the card. So I'll be on the lookout for red cards as it has a higher chance of being open than other colors based on the texture of this pack.
This draft ended in a completely different manner than you would expect. I actually ended up in W/B Vampires! I ended up getting a near-last-pick Queen's Bay Soldier in pack one, and got passed a pick-four Sanctum Seeker in pack two, took it to hedge towards U/B, and then got passed Call to the Feast and Bishop's Soldier. At this point I thought there was a reasonable chance there were no Vampire drafters at the table, and I moved in (note I still had the option to back up into U/B should I be wrong, maybe splashing Call to the Feast off of treasures). I was correct in my assumption and wheeled all the Vampire cards for the rest of the draft, and continued on to a trophy.
Takeaway: Don't put on your blinders in this format.