Abilities: 

First, convert the character's stats using the Attributes chart.

Second, convert each of the character's chosen skills by taking their current skill, minus the ability modifier, minus 3 (because a first level character can start with 4 in a given skill).  The result should be equal or less than the character's level.  If less than 0 after the conversion, then the skill is 0 + ability.

Example:  A 5th level cleric with 18 WIS has "Heal" at 12
    8 ranks + 4 ability modifier

D6 rank is 12 - 4 - 3 = 5, which is the character's D20 level.

Add the skill to the ability score to get the final skill level.

Using the example above, the character's Heal skill would be 4D+5, which converts to 5D+2.

For weapons skills, convert the Base Attack Bonus directly.  A 10th level fighter gets +10 in weapons he is proficient with, our 5th level cleric gets +3 added to his ability for his weapon skills.  Convert magic skills similarly.  An 8th level mage gets his spell skills at +8.

Saving throws convert to these skills:  Reflex into dodge, Fortitude into "Physical Resistance", Will into "Mental Resistance".

Finally, you can customize the character more by taking from one skill and adding to another.  Do this by converting skills diminished to character points, and using those to increase other skills.  For example, it takes 12cp to increase a skill from 4D to 5D, decreasing a skill fom 6D to 5D+1 frees up 10cp.

If creating a new character based on D20 level, the character gets 3D in starting skills per level.  I.E if the player wants to create a new character who is roughly equal to a 6th level D20 character, he would get 18D to by skills.  (This is also an alternate method for converting characters from D20.)

Feats

Converting feats is more subjective.  For feats that enchance a skill, just add the bonus to the current skill and forget about the feat.  For other feats, consult with the GM.

Magic

Each school of magic or cleric domain is a separate skill.  In addition, a spellcaster also gets an amount of spell points, which regulate how much and how often they can cast spells.

Magic Points = Highest magic skill, in pips

For example, a spellcaster with an Enchantment of 6D gets 18 spell points

Spells cost 1 spell point for a successful casting.  If the spellcaster fails in casting a spell the cost is the target difficulty - the actual roll.

Saving throw difficulty versus spells is 10 + spell level, i.e. 15 for a fifth level spell.  The DC increases if the caster did exceptionally well on their skill attempt.  For each 5pts a caster exceeds the spell difficulty, the saving throw DC increases by +1.

Characters get at least one spell per D level in each domain, more if the GM permits.

Generally speaking, magic damage is 1D per spell level.  When converting a spell's effect, spell level is the level in D, caster level is determined the same way as spell points are (Skill - 2D, in pips), but unlike spell points caster level is calculated individually for each spell skill.

Items

Weapon damages are presented in a separate chart.

Armor is converted by taking the armor's base AC and converting to pips.  Armor check penalties are converted the same way.  Armor check penalties apply to dexterity, movement, attack, and spellcasting skills when performed wearing the armor.

Example:  Full Plate is +8 AC, -6 penalty in D20, which translates to +2D+2 Armor, -2D penalty in D6

Armor and weapon enchantments are similar, one pip per plus.  A longsword +3 is a longsword +1D.

Magic items that give enhancements to abilities:  Diving the enchantment by half.  A cloak of charisma +4 becomes a cloak of charisma +2.