As a student of a beginners' Japanese class, I was aware of only one way to master the shapes of kanji: brute, forced memory. I dutifully wrote the assigned kanji --over and over-- in the little squares provided in my workbook. Every "100" I scored on a weekly quiz made me feel confident that I was headed toward literacy in Japanese.
Yes, I was one happy kanji camper-- until a distressing obstacle came along:
look-alike kanji. At first, remembering 天 was a breeze. That is, until
my sensei assigned 夫. Then up popped 矢 and 失. Ouch!
For a while, especially after Japanese word processors and then computers
became part of my everyday life, I consoled myself with this notion: "I
won't be writing kanji very often, so just being able to recognize them
will suffice." Increasingly, however, look-alike kanji became impediments
to rapid reading, particularly when they appeared in unfamiliar compound
words. I lacked the ability to analyze the detailed features of strikingly
similar characters like 犬/ 太, 連/運, 理/現, 数/類, 困/因/囚, 賃/貸/資/貨/貧,
則/側/例/測, 祭/察/際, 線/緑/録, 輸/輪, 熱/勢/熟/塾, 歓/勧/観/権/確, and
so on.
Frustration with look-alike-kanji was a major factor in my taking a break of several years from serious kanji study. I eventually got back on the track towards literacy in nihongo, however, with the discovery of several excellent kanji self-instruction books that employ "component analysis." I learned to stop viewing kanji as whole units and instead to start using my adult powers of logic to analyze their component parts.
Using component analysis, a student systematically divides each character
into mini, manageable elements made up of anywhere from one to six strokes.
Some component names (e.g., 木 for "tree" and 斤 for "ax")
are based on ancient Chinese explanations. Others, such as "dollar
sign" 
and "sunglasses" 
, are arbitrarily and even humorously drawn from our contemporary daily
life.
A kanji learner can recall the shapes and meanings of look-alike characters by linking their components together in vivid stories like these:
天/夫/矢/失
天 sky/heaven
The sky is a kind of "ceiling"一, a particularly "big" 大 one. (Note that when handwritten, the uppermost stroke of 天 may be shorter
than the stroke below it).
夫 husband
I can see my husband's "head" 
sticking up above the "sky" 天. He always has his "head" in the clouds!)
矢 arrow
That flying "object" 
way up in the "sky" 天 is an arrow.
失 lose
My "husband" 夫 is always losing things. Some "object" , probably his wallet, is ready to fall from his left side.
則/側/例/測
則 rule
An ancient rule-maker (a ruler) had "money" 貝 (shells, used instead of coins) and a "sabre" 
.
側 beside
In those days, "people" 
stood beside their "rulers" 則 -- if they valued their lives!
例 example
"People" were required to make regular visits to the tombs of exemplary military heroes. Each tomb contained "bones" 
and a "sabre" .
測 fathom/measure
A "water-ruler" (
plus 則) measures fathoms.
Some of these stories spring from the imaginations of three of my favorite kanji storytellers: Joseph De Roo ("2001 Kanji"), James Heisig ("Remembering the Kanji"), and Mark Donaghue ("KanjiCan" software). Their kanji tales have become woven together--along with some of my own creation-- in an intricate, personal road map for remembering the shapes of all the nearly 2,000 general-use characters.
If you are just setting out on a kanji-learning journey-- or, perhaps, have become lost along the way-- I urge you to use component analysis. Take the time to equip yourself with a map for masterfully analyzing kanji shapes, and you will find yourself cruising down the kanji highway, navigating with ease those former roadblocks: look-alike characters.
To learn more about a variety of kanji learning materials that utilize component analysis, please go to Book Reviews on this site.