Identify your use case: sandwich/grilled, baking/gratin, or stir-in sauce; this determines the best texture/melt match.
Choose the substitute that matches your need (mild creamy melt for best results), then measure using the listed ratio (by weight if possible).
If the substitute is drier/firmer (Swiss-style, provolone), shred or thin-slice to improve melting and distribution.
If the substitute is softer/wetter (American, Muenster), use the ratio and avoid overcooking—melt quickly and can go oily.
Taste and adjust in context: add a small pinch of salt for bland swaps, or balance tang by using a slightly richer sauce/dough.