Start with floor space and safety
A terrestrial enclosure should prioritise floor area over height. Heavy-bodied tarantulas are not designed to fall from the top of a tall glass tank. Use enough substrate to keep the distance from substrate to lid low and remove hard objects that could turn a short fall into an abdominal injury.
Substrate depth
Give enough compacted substrate for the spider to dig or modify a retreat. Even species described as terrestrial often excavate when young. The substrate should support a burrow rather than collapsing as soon as the spider starts moving it.
Hide and water
A half-buried cork hide gives a useful starting retreat. Add a stable water dish and keep it filled. The dish can be shallow; a healthy tarantula is not going to drown in an appropriately sized open dish.
Moisture strategy
Species differ, so avoid one universal humidity target. Dry-country terrestrials can have mostly dry substrate, while moisture-dependent species need deeper damp layers or a gradient. Good ventilation matters in both cases.
Decor and access
Keep decor simple and stable. Plants and leaf litter can look good, but every object should either provide cover, help web anchoring or be easy to clean. Do not block the keeper from reaching the water dish or safely using a catch cup.
Maintenance
Spot-clean boluses, dead feeders and obvious mould. A full substrate change is not routine maintenance for a healthy enclosure. Disturb the spider as little as practical and preserve a settled retreat whenever possible.