Let me summarize them for you:
Right-align your numbers
Left-align your texts
Use decimals appropriately (one or two is often enough)
Display units (e.g., $, %) sparsely (e.g., only on first row)
Highlight outliers
Highlight column headers
Use subtle highlights and dividers
Use white space between rows and columns
Use white space (or dividers) to highlight groups
Use visualizations for large tables