How to play Spider solitaire well once you know the rules: the decisions that matter, and the habits that win.
Any card can go on a card one rank higher, but only a run of one suit can move as a unit. A mixed pile of seven cards is seven cards you will have to take apart one by one, and you will often not have the space to do it.
When two moves are otherwise equal, always make the one that stays in suit. When an off-suit move is the only way forward, make it where it is easiest to undo, on top of a column you are not relying on.
An empty column takes any card or any suited run, which makes it the only tool for rearranging mixed piles. One empty column lets you move far longer runs than it looks, because you can park part of a sequence, shift the rest, and bring the first part back.
Work towards emptying the column with the fewest cards in it, and once you have a space, do not fill it with a single card just because you can. Use it to sort something out, then clear it again.
Every column starts with its cards face down except the last. Prefer moves that turn a card up, and favour the columns with fewer hidden cards, because those are the ones you can finish clearing.
Kings deserve special attention. A king can only move into an empty column, so a king turned up at the top of a short column is good news, and one turned up with cards still hidden beneath it is a column that stays locked.
Dealing puts a card on every column, burying whatever you had arranged. Before you deal, make every useful move and put the columns in the best order you can, with suited runs on top where the new cards will disturb them least.
You may not deal while a column is empty. If you have cleared one and are about to deal, fill it with something that will be easy to move again — not with a king you will never get back out.
The table deals two suits by default. One suit is almost always solvable and a good place to practise the habits above; four suits is hard enough that careful play wins only some of the time.
At every level the same thing decides the game: how many empty columns you have when the stock runs out. Count the deals left, and play the last ones more slowly than the first.