One player, a clear layout and a little time.
Choose a named version
Solitaire, also called patience, describes many single-player card games. The layout, permitted moves, stock and winning condition depend on the version. Start with a complete rule set rather than combining remembered rules from different games.
Set up carefully
Check the number of decks, the initial layout and which cards begin face down. Agree with yourself how redeals and undoing moves will work before starting, especially when comparing results between sessions.
Notice decisions, not just outcomes
A finished game can be useful even when it does not end in a win. Record which choices opened useful spaces or blocked access to a needed card. Not every deal in every version is necessarily solvable.