Start with the corners and edges
The border is the tightest part of any Filoop board. Fewer neighbours mean fewer choices — and fewer choices mean moves you can be sure of.
Count the neighbours
A cell in the middle of the board touches four others. A cell on the edge touches three, and a corner cell only two. When you look for a safe move, look where the choice is smallest: the border.
A thread that passes through a cell uses two of its neighbours — one to come in, one to go out. A corner has exactly two, so a thread that passes through a corner has no options at all: it comes in along one edge and leaves along the other.
Buttons in corners
A button in a corner can leave in only two directions. Often one of them is blocked right away — by another button, by a finished thread or by a cell that clearly belongs to someone else. Then the first step is free. Take it.
Even when both directions are open, a corner button tends to run along the edge for a while. Turning into the middle early leaves a strip of border cells behind it, and such strips are hard to fill later: every cell along the edge still needs a thread to pass through it.
Don’t leave a corner behind
The opposite mistake is just as common. If a thread passes next to an empty corner and takes one of its two neighbours, the corner has one free neighbour left. A thread could enter it but never leave, so only the end of a thread — a button — could sit there. No button, and the board can’t be finished.
Before you draw past a corner, ask yourself who will fill it. If the answer is “nobody”, route the thread through the corner instead.
Work inward
On a real level, go around the border first: corners, then buttons on the edges, then the cells between them. Each finished piece of border turns the next ring of cells into a new edge — with fewer neighbours and fewer choices again.
Stuck in the middle of a level? Go back to the border and count the neighbours again — the next sure move is often there.
Next: forced moves, where one sure step leads to the next. The rules in short are on how to play. Try it all on the warm-up set, whose levels are solved by forced moves alone.