Playing Double Solitaire well
In brief
The 36 face-down cards decide the game: play first what uncovers them, especially in the longest columns. Every card exists twice: when a spot is missing, its twin may be elsewhere. Only empty a column if a king can go there.
1. Uncover the face-down cards
A face-down card can't be played and can block an entire suit. Between two possible moves, prefer the one that flips a card, and think about the columns on the right: column 9 hides 8 cards at the start.
In the deal DS1-D1N-AAAAAAB, the won game begins by moving the top of column 4, which flips the A♦. On move 2, that ace goes up to its foundation: it earns 10 points, flips one of the 2 cards still face down in the column (5 more points) and the score goes to 20. 34 face-down cards remain.
Stock: 59 cards; waste empty. Foundations, cards placed: 0 spades, 0 hearts, 0 diamonds, 0 clubs, 0 spades, 0 hearts, 0 diamonds, 0 clubs. Column 1: 0 face down, then 2 of hearts; column 2: 1 face down, then jack of diamonds; column 3: 2 face down, then 2 of spades; column 4: 3 face down, then 8 of spades; column 5: 4 face down, then 9 of hearts; column 6: 5 face down, then jack of clubs; column 7: 6 face down, then 9 of clubs; column 8: 7 face down, then queen of diamonds; column 9: 8 face down, then king of diamonds.
2. Use the duplicate cards
With two decks, every card has a twin: a black 6 can be placed on any of the four red 7s (two 7s of hearts, two 7s of diamonds). When a card is waiting for a spot, look for where its twin is, or the twin of the card that would take it. The 8 foundations, two per suit, also let two sequences of the same suit be built up at the same time.
3. Keep the empty column for a king
An empty column accepts only a king. Emptying it with no king ready to go there is pointless: the card that occupied it could have received a sequence. Empty a column when a king is waiting, preferably a king placed on face-down cards. The Examples page shows the 2♥ refused on an empty column.
4. Don't build up too early
Aces and 2s can go up without risk. Higher up, a card placed on a foundation can no longer receive a card on the tableau: a 5 of hearts moved up too fast is then missing to take a black 4. The app never moves anything up on its own, precisely to leave you that choice. If needed, the top card of a foundation can be taken back to the tableau.
5. A thick stock: limit recycling
The stock has 59 cards. In Normal scoring, each recycle of the waste costs 100 points: before turning the stock over, play everything that can be played. With draw 3, only one card in three is directly playable on each pass, and playing a card from the waste shifts the following ones. The same deal required 1 recycle with draw 1 (DS1-D1N-AAAAABA) and 5 with draw 3 (DS1-D3N-AAAAABA) in the won games on the Examples page.
6. In Vegas, a single pass
In Vegas, the stock can be gone through only once. Before each touch of the stock, make all the useful moves on the tableau: a covered waste card won't come back. The score starts at -$104: you need 21 cards on the foundations to get above zero.
7. Use undo
The app keeps the last 200 actions. When two moves seem equally good, try one, look at the card it uncovers, and undo if it doesn't help: undoing also removes the points from the move.