In the Magic: the Gathering commander format, players build 100-card decks with every card (apart from basic lands) only appearing once. The format is primarily played with four players, each with their own deck.

In creating a Magic: the Gathering Commander deck, it needs great planning and thought in coming up with an efficient decklist and strategy. Here are some guidelines to keep in mind while building an effective Commander deck:

1. Choose a Commander: Select a Legendary creature as your Commander. This choice will dictate the colors and theme of your deck. Consider your preferred playstyle and the abilities of the Commander when making your selection.
2. Determine the Theme or Strategy: Decide on the theme or strategy you want your deck to revolve around. It could be tribal, control, aggro, combo, or any other concept that appeals to you. Having a clear focus will guide your card choices and deck construction.
3. Establish a Mana Base: Determine the appropriate number of lands and mana-fixing cards for your deck. A good starting point is around 36 to 40 lands, but adjust based on your mana curve and the mana requirements of your cards. Include mana rocks and other ramp cards to ensure consistent mana production.
4. Select Synergistic Cards: Choose cards that synergize with your chosen Commander and overall theme. Look for cards that support your strategy, provide card advantage, or disrupt opponents’ strategies. Consider including cards that interact with your Commander’s abilities or promote the overall game plan of your deck.
5. Manage Your Mana Curve: Aim for a balanced mana curve with a mix of low-cost, mid-range, and high-cost spells. Having a smooth curve ensures that you have playable cards at every stage of the game. Be mindful of having enough early-game interaction and sufficient late-game threats.
6. Include Removal and Interaction: Ensure your deck has a good amount of removal spells and interaction to deal with threats and disrupt opponents’ strategies. Include targeted removal, board wipes, counterspells, and other forms of interaction that suit your deck’s colors and theme.
7. Consider Card Draw and Card Advantage: Include cards that provide card draw and card advantage to maintain a steady flow of resources. Look for spells that allow you to draw additional cards, tutor for specific cards, or generate value over time.
8. Fine-tune and Test: Once you’ve assembled your deck, playtest it against different opponents and adjust as necessary. Pay attention to the performance of individual cards and the overall synergy and effectiveness of your deck. Make adjustments based on your playtesting experiences.

Remember that building a Commander deck is a creative process, and personal preferences play a significant role. Experimentation and adaptation are key as you refine your deck over time. Have fun exploring different strategies, discovering new synergies, and customizing your deck to suit your playstyle.