I feel it depends on a few things:
- Are there any new things to teach, or is this just about easing people into the pack? In the latter case, I've recently started to prefer not doing this, which is why my newer packs (LPIV, LPV and especially LPO2) have less such levels, and put more emphasis on relatively-easy puzzles than X-of-everything levels. Likewise, if LPVI ever comes, I suspect it too will have very few, if any, X-of-everything type levels.
- Are we teaching something relevant to almost every level, or at least a large number of levels, such as a new skill? If so, introduce it as soon as possible. LPO's first 7 levels are like Orig's first 7, in that they each introduce one (or two) new skills and are easy levels to focus on the use of that skill. LPO2, which was the first pack to use the Fencer, introduced it on the second level, then the third level was an X-of-everything (one of only two X-of-everything levels in the pack, and the other was a somewhat gimmicky level) that included Fencers as one of the available skills.
- Or are we teaching something that'll show up from time to time but not too often, such as a new object? If so, it should still be introduced relatively early, but doesn't have to be right away. LPIII, which by far introduced the most new objects, spreads the new object tutorials throughout the first rank. Although on the other hand, LPIV which introduced (anti)splat pads and single-use traps, had the tutorials on the 2nd and 3rd levels.
- Or are we trying to teach a trick? I often don't do a tutorial for this at all, instead, it needs to be figured out in the level where it's actually relevant. With that being said, sometimes I do hint at this...
An example would be the Spiky level, "Don't Forget". This level uses - not necesserially teaches as such - a trick where a platformer is placed across a gap, then another platformer is placed across the gap slightly higher, so a basher can bash across the platform without stopping. The level title hints at that this trick may be used again in a later level - and indeed it is, in Sharp 17 "Broken Arrow", where it's much more well-hidden than in "Don't Forget".