Theros is a large set with 101 commons, 60 uncommons, 53 rares, 15 mythic rares, and four variations of each standard basic land. This is the normal size for a large set of this era. Foil cards are included in booster packs with advertised odds of 1 : 67 cards. The set was printed in English in the USA and Belgium.
Theros was sold in 15 card booster packs (which contain an additional ad card). Booster boxes have 36 packs.
The US printing uses sequential collation with C1/C2 common collation.
Packs are back-facing and have 10 commons followed by 3 uncommons, a rare, a basic land, and an ad card. If there is a foil card, it will appear after the rare, displacing a common.
|10 Commons||3 Uncommons||1 Rare||1 Land||1 Ad Card|
|9 Commons||3 Uncommons||1 Rare||1 Foil||1 Land||1 Ad Card|
Packs are evenly split between C1 commons and C2 commons. C1 packs have 2-3 A cards, 2 B, and 4-5 C. C2 packs have 4 A cards, 2 or 4 B, and 2 or 4 C.
When a foil appears in a pack, it will displace a common card. Common foils displace A commons and only appear in C1 packs. Uncommon foils displace B commons. Rare foils displace C2 commons.
Uncommons are printed on one sheet with each card appearing twice (and one filler). This is divided into a 66-card A run (with 33 distinct cards) and a 54-card B run (with 27 distinct cards). Packs can have either 2 A cards followed by 1 B card, or 1 A card followed by 2 B cards. Since the runs are unbalanced, 2 A cards should mathematically happen 13/20 of the time.
The A common run consists of 33 different cards each appearing twice. The choice of first card is mostly arbitrary.
The B common run consists of 22 different cards each appearing three times. The choice of first card is mostly arbitrary.
The C1 common run consists of 27 different cards each appearing twice plus Unknown Shores, the short-printed common. The choice of first card is mostly arbitrary.
The C2 common run consists of 18 different cards each appearing three times plus Unknown Shores, the short-printed common. The choice of first card is mostly arbitrary.
The A uncommon run consists of 33 different cards each appearing twice. The choice of first card is mostly arbitrary.
The B uncommon run also consists of 27 different cards each appearing twice. The choice of first card is mostly arbitrary.
Most of the marketing cards in Theros have a token, tip, or emblem on the front face. In addition, there is a card that has an advertisement for Magic 2014 on the front face. (The front has an PEGI rating and the back has ESRB, so I'm not aware of any region differences.) They are printed on an 11 × 11 sheet with different items appearing different numbers of times. The choice of first card is mostly arbitrary.
|Cleric × 1||Elspeth, Sun's Champion Emblem × 1||Bird × 2|
|Satyr × 2||Elemental × 3||Commander Tip Card × 5|
|Elspeth Tip Card × 5||Golem × 5||Legendary Permanents Tip Card × 5|
|Xenagos Tip Card × 5||Bestow Tip Card × 6||Boar × 6|
|Enchantment Creatures Tip Card × 6||Gods Tip Card × 6||Heroic Tip Card × 6|
|Monstrous Tip Card × 6||Soldier × 6||Harpy × 8|
|Duels 2014 Ad Card × 10||Soldier × 12||Soldier × 15|
There was a picture of the foil common sheet available.  Each common card and each basic land variation appears once.
 The common runs for US Theros were originally posted by Medussa on the MTG Salvation forums.
 A picture of the foil US common sheet was available in the collection of Casey Petrillo. (This collection is no longer publicly accessible.)