Turn Structure
by nfin8e

The table below shows the structure of a single turn from start to finish. The first column contains the five phases of the game (Beginning, Precombat Main, Combat, Postcombat Main, and End). The second column has the steps that are in each phase (note that the main phases don't have any steps). The third column lists the actions that must be taken in that step in order. (Updated to reflect Comprehensive Rules of July 1 2003.)
Legend for all noted steps

A.  Current player chooses the order that triggered abilities that go on the stack.
    
   B.  Game checks for state-based effects first, whenever a player recieves priority.

Magic Turn Structure

Beginning Phase Untap Step "At Beginning of Turn" and "At Beginning of Untap Step" triggered abilities trigger, but they do not go on the stack until the beginning of the Upkeep Step.
Phasing happens. All phased out cards phase in and all cards with Phasing which are in play phase out simultaneously.
Current player untaps all permanents he controls.
Upkeep Step "At Beginning of Turn", "At Beginning of Untap Step", and "At Beginning of Upkeep" triggered abilities trigger. A
The current player gets priority to play instants and activated abilities. B
Draw Step Active player draws a card. (This action does not use the stack.)
"At Beginning of Draw Step" triggered abilities trigger. A
The current player gets priority to play instants and activated abilities. B
Check for Mana Burn.
Precombat Main Phase "At Beginning of Main Phase" triggered abilities trigger. A
The current player gets priority to play instants and activated abilities. B
When the stack is empty, the current player may play lands, creatures, and sorceries.
Check for Mana Burn.
Combat Phase Beginning of Combat Step "At Beginning of Combat" triggered abilities trigger. A
The current player gets priority to play instants and activated abilities. B
Declare Attackers Step The current player declares his attackers. If no attackers are declared, then skip the rest of this step, the Declare Blockers step, and the Combat Damage step. Go directly to the End of Combat step.
Triggered abilities that trigger off attackers being declared trigger at this point. A
The current player gets priority to play instants and activated abilities. B
Declare Blockers Step The defending player declares his blockers and which attacking creatures they will block.
Triggered abilities that trigger off blockers being declared trigger at this point. A
The current player gets priority to play instants and activated abilities. B
Combat Damage Step First Strike Combat Damage If no attacking or blocking creatures have First Strike, then skip this entire section.
The current player announces how the attacking creatures that have First Strike will deal their damage.
The defending player announces how the blocking creatures that have First Strike will deal their damage.
All combat damage from creatures with First Strike goes on the stack as a single unit.
The current player gets priority to play instants and activated abilities. B
After all spells and abilities have resolved, combat damage from creatures with First Strike resolves and is dealt simultaneously to each creature as it was originally assigned.
"Deals Combat Damage" and "Is Dealt Combat Damage" triggered abilities trigger. A
The current player gets priority to play instants and activated abilities. B
The current player announces how the attacking creatures without First Strike will deal their damage.
The defending player announces how the blocking creatures without First Strike will deal their damage.
All combat damage from creatures without First Strike goes on the stack as a single unit.
The current player gets priority to play instants and activated abilities. B
After all spells and abilities have resolved, combat damage from creatures without First Strike resolves and is dealt simultaneously to each creature as it was originally assigned.
"Deals Combat Damage" and "Is Dealt Combat Damage" triggered abilities trigger. A
The current player gets priority to play instants and activated abilities. B
End of Combat Step "Until End of Combat" effects end.
"At End of Combat" triggered abilities trigger. A
The current player gets priority to play instants and activated abilities. B
Check for Mana Burn.
Postcombat Main Phase "At Beginning of Postcombat Main Phase" triggered abilities trigger. A
The current player gets priority to play instants and activated abilities. B
When the stack is empty, the current player may play lands, creatures, and sorceries.
Check for Mana Burn.
End Phase End of Turn Step "Until End of Turn" effects do not end at this point, they end during of the Cleanup Step.
"At End of Turn" triggered abilities trigger. A
The current player gets priority to play instants and activated abilities. B
Cleanup Step The current player discards down to his maximum hand size (usually seven).
Simultaneously remove all damage from permanents and end all "Until End of Turn" effects.
Check for state-based effects.
Any triggered abilities that have triggered since the beginning of the Cleanup Step are placed on the stack. A
If any state-based effects were resolved or if any triggered abilities were put on the stack, then the current player gets priority to play instants and activated abilities. If this occurs, then once the stack is empty, rather than going to the next turn, a new Cleanup Step begins. This loop continues until there is a Cleanup Step in which no state-based effects are resolved and no triggered abilities are placed on the stack.
Check for Mana Burn.