Rule #1: Clarity of Spelling.
0 (zero), O (cap 'o'), 1 (one), I (cap 'i'), and l (lowercase 'L') are all toxic. AV0lD THEM AII.
Also try to avoid ambiguous spellings, or letters that together look different like LI and U or 'rn' does with 'm'.
Same with Unicode, typos or weird phonetic substitushuns. Avoid switching 'ph' with 'ff' and the like.
Rule #2: Shorter is better.
Try to avoid incorporating titles or excessively long words in your name... like SirMarvingtonTheThird or GwendolynChrysanthemum
Rule #3: Puns / humor are great, but pick a name that fits your temperament. Silly, Serious, Snarky, Aloof, Hyper, ... try to figure out what one word others would use to describe your personality and ask yourself if the name you picked conveys it.
Two simple names separated by a space are often more memorable / descriptive than a single but more complicated word.