NB: to keep the article short and concise, I’ll assume that the reader has a pop-up Chinese dictionary installed, giving meanings and pronunciations. I recommend "Mandarin popup" with Firefox.

1 象形字 Pictograms
These characters represent the meaning of the object, with direct depiction: 山, 行, 土,火,水, 川, 州,雨, 屮, 竹, 米, 禾, 人, 士, 夫, 大, 女, 母, 子, 儿, 齿, 舌, 耳, 毛, 乃, 也, 肉, 止, 之, 彳, 足, 甲, 龟, 鱼, 马, 牛, 羊, 犬, 鸟, 贝,刀, 戈, 弓, 伞, 串, 矢, 矛, 盾, 门, 高, 巠, 酉, 瓦, 丝, etc.

The meaning of these has drifted towards more abstraction:
日 sun for day, 月 moon for month, 木 tree for wood, 金 bell for gold, 面 face for side, 首 head for chief, 页 head for page,口 mouth for opening, 言 tongue for speech, 自 nose for self, 目 eye for item, 手 hand for activity, 心 heart for mind, 正 foot for uprightness, etc.

2 指事字 Simple Ideogram
They represent more abstract concepts, either by some symbolic shapes 一, 二, 三, 八, 十, 廿, 卅, 世, 力, 丄, 上, 丅, 下, 工, 示, 方, 回, etc. or by using a stroke to point at the part of an existing pictogram: 本, 末, 刃, and 血, 太?

3 会意字 Combined Ideogram
These are also ideographic, and are formed by the combination of 2 or more pictograms, to form a situation: 信 (trust the words of a person), 武 (foot and axe), 林, 森, 休, 明, 男, 字, 岩,莫 (日+艸 sunset into the grass), 事, 吏, 史 (口+丨+又 a hand writes down the words of a mouth), 及 (又+人 a hand grabs a man),是(日+正 straight under the sun: exist here and now), 道(首+辵), 烦, 播, 多(月+月 2 moons is too much!), 半(牛+八 an animal split in two halves), 出 (屮+凵 a sprout arises from a pot) , 去 (大+凵 a man leaving a enclosed area), 走 (大+止 a man walking with foot),内 (入+冂 open the door curtains ), 关/關(門+丝+廾 hands closing door curtains), 开/開 (門+廾+一 hands lifting a door bolting bar), 名(夕+口 a mouth calls the name at night for identification),集 (birds on a tree), 看 (hand over the eyes), 采 (hand collecting fruits), 令 (mouth commanding to a kneeling man), 葬 (hands carrying a dead under grass), 只/隻 (a single bird in hand), 双/雙 (2 birds in hand), etc.

4 形声字 Phono-semantic compound
This is the most frequent method, where 2 characters are joined, one bringing the meaning and the other the pronunciation.

Unusual examples: 在=才+土, 青=井+生

Some use rare semantic keys which have interesting intrinsic meanings:

  • 十 for Wholeness and harmony: 协, 叶, 博, 章, 卓
  • 方 for Movement: 旅, 斿, 游, 旋; Give: 施, 於(于), Flags: 旄, 旗, 旆, 旐, 旓, 旛, 旝, 旟, 旃, 旎, 旌, and Group identity: 族, 圀 (It is remarkable that 方 nearly always comes with the component丿一)
  • 羊 for Virtue: 美, 善, 義, 對,盖,reach: 達,着 but also negative: 羞,差,蹉,傞...
  • 页 for Head: 頭,领,顶,颠,项,额,颜,颈,颅,颊,颌,颏,颐,顸,颡 Head emotions: 烦,顽,顼 Head abstract: 预,倾,顾,顺,顿,颁,颂 Importance: 须,题,硕,颀,颉,颢,灏,颛

The key 月 generally refers to 肉, indicating a part of the body. In few rare cases it refers actually to the moon 月: 期, 明, 望, 阴, 朗, 塑, 朔, 朝. and 服?肯?

5 假借字 Phonetic loan
This group is interesting in that it debunks many myths about ideographic etymology. It is the only one where there is (a priori) no semantic link between the graphical and semantic content.

The construction scenario consists in using a character to represent another word which has a similar pronunciation, like a rebus. In English, SMS aficionados would write “This is 4 you”, because “four” and “for” are considered phonetically interchangeable. Later, the borrowed character, now being used for two completely different meanings, would typically be given a semantic key when used for its original meaning, becoming a kind of usurped word that has to wear this key to reassert its original meaning! (e.g. 四originally depicts nostrils to mean “mucous”. Now it means “4” and "mucous" is added the water key氵to become 泗)

However if some semantic connection exists between the 2 meanings, the pair could be regarded as what I propose to call a 变意字: semantic variation.

  • 枼 “flat”, originally “leaf”, which is now 葉 (Possible links between “leaf” and “flat”)
  • 北 “north”, originally “back”, which is now 背(Possible link if the Emperor was supposed to face south)
  • 少 “few”, originally “sand”, which is now 沙 and 砂(Possible link between “few” and small grains of sand)
  • 来”come”, originally “barley”, which is now 麥(Possible link between “coming” and the advent of a crop)
  • 莫”do not”, originally “sunset”, which is now 暮 (Possible link between sun disappearance and negation)
  • 四”4”, originally “mucous”, which is now 泗
  • 要 “demand”, originally “waist”, which is now 腰
  • 東 "east", originally "heavy bag", which is now 重
  • 永 “eternity”, originally “swim”, which is now 泳
  • 又”again”, originally “right hand”, which is now 右
  • 亦 "also", originally "armpit", which is now 腋
  • 也 "also", originally "snake" interchangeable with 它, which is now 蛇

6 转注字 Derivative cognate
Smallest group and least understood. A word would evolve into 2 distinct meanings and be graphically modified to indicate this difference to account for this split. The akin characters therefore have all 3 similarities, of meaning, sound, and shape. The graphical modification doesn’t use semantic key like 变意字 but rather directly modifies the shape of the character. The only certain example so far is 考 “examine” and 老 “old”.

I suggest considering the kinship of shape, meaning and sound between: 之, 彳, 辵, 止, 夂, 正, and 是, and then between 事 and 史.

From observation, I’ve come to identify 3 more categories, somehow related to "3.会意字" and "6.转注字":

33 二代会意字 Secondary Combined Ideogram
This category contains the characters formed of 2 parts, both indicating the meaning, but without the pronunciation of any of the two. The construction method has 2 steps of combined ideogram:

  • First 亼+口 => 合, then 合 => 答, 洽, 䆟, 恰, 拾, 拿,容
  • First 止+止 => 步, then 步 => 涉 wade through, 陟 ascend => 骘 promote
  • First 隹+木 => 集, then 集 => 襍 雜 (杂)
  • First 羊+工 => 差, then 差 => 蹉, 傞
  • First 人+匕 => 化, then 化 => 倾

63 变意字 Semantic Variation
Those characters have all 3 similarities (sound, sense, shape) but are obtained through additions of keys:

  • 夬 => decision: 决, resolute speed: 快 趹 駃,take: 抉 刔 pierce: 鈌 䆢 䆕 䦼, fork: 筷, parting: 诀
  • 仑 => 论, 伦 , 轮 (regular cycle, cf 法轮)
  • 合 => 盒, 蛤, 颌
  • 答 => 搭
  • 容 => 熔
  • 女 => 如 (women follow father, husband, and son), => 努
  • 厄 => 阨, 危, 脆, 㧪, 垝, 卼, 峞
  • 臤 => hard: 坚, 紧, 㹂, 䃘 wise: 贤, 竖, 㷂
  • 亡 =>忘, 盲, 巟, 荒
  • 莫 => 寞, 漠, 墓
  • 正 => 证, 整, 政
  • 工 => 功, 贡, 项
  • 才 => 材, 财
  • 旨 => 指, 恉
  • 步 => 頻 frequency,濒 approach
  • 方 => 房 square room, 坊 city quarter
  • 令 => 命
  • 分 => 份
  • 州 => 洲
  • 廷 => 庭
  • 原 => 源
  • 元 => ?頑: obstinate, play, 玩, 完 (antonym)
  • 知 => 智, 痴 (antonym)
  • 贯 => 惯
  • 度 => 渡
  • 并 => 拼
  • 气 => 汽,忾,饩,㔕
  • 道 => 导
  • 王 => 皇
  • 酉 => 酒
  • 厶 => 私
  • 從(从) => 蹤(踪)
  • 力 => 勒, 劳, 励
  • 反 => 返, 叛, 㤆
  • 执 => 势
  • 连 => 链
  • 曼 => 漫, 蔓, spreading time: 慢, 䟂
  • 长 => 张, 胀
  • 买 => 卖
  • 告 => 造 (summon to create)
  • 单 => 阐 (plain, explain), 禅
  • 素 => 愫
  • 贵 => 匮 (scarce hence valuable)
  • 至 => 致
  • 人 => 仁 (human and humane)
  • 又 => 有 (hand, having)
  • 直 => 植, 殖
  • 占 => 站, 店, 点, 贴 (occupied place)
  • 包 => 袍, 抱, 胞, 泡, 疱, 匏, 饱
  • 官 => 馆, 管
  • 主 => 住, 驻
  • 朝 => 潮 (dynasty, time, tide)
  • 生 => 性, 姓,甡,產,甦(苏)
  • 支 => 枝, 肢, 歧, 技,伎
  • 辟 => 闢, 壁, 避
  • 保 => 堡, 葆, 媬
  • 井 => 青 => green 菁,clear and calm 晴, 静,靖,靓,清,婧,䨝
  • 井 => 阱,穽,汫
  • 夹 => 陕,挟,峡,䇲
  • 昜 => sunlight 旸, 陽, 砀, burn: 烫, 汤, 炀, 疡, 肠, wide open: 场, 畅, 扬, 颺, 蕩
  • 夗 => turn, bend: 宛, 婉, 蜿 wrist and knee: 腕, 捥, 踠 , bowl: 碗, 剜
  • 户 => light door or fan: 扇, 煽, 煸, 谝 , bamboo door panel: 扉 扁 set of bamboo slips: 篇, 编, 雇, open door: 启 肇, shelter: 护, 庐 fireplace/foyer: 炉 (after simplification)

66 只声转注字 Phonetic Cognates
Besides, there are also many words with similar pronunciations and meanings, as if a common ancestor in spoken language had generated them after semantic variations, using various characters. This is not really a generation mechanism, but rather a kinship between characters.

  • 无, 毋, 勿, 莫, 寞, 漠, 默, 唯, 惟, 未, 没, 歾, 末, 貉, 墓, 缪, 穆,and also 误, 污, 怃 ?
  • 不, 否, 弗
  • 和, 合, 协, 劦, 勰, 叶, 旪, 谐, 龤, 偕, 燮, 爕
  • 副, 扶, 辅, 附
  • 综, 统, 总, 丛, 同
  • 原, 源, 元, 缘, 爰
  • 任 (allow) 认 (admit) 忍 (tolerate)
  • 相, 像, 象
  • 穿, 串, 贯, 惯
  • 他, 她, 牠, 它
  • 我, 吾, 余, 予, 卬
  • 工, 功, 贡, 供
  • 义, 意
  • 扩, 阔
  • 监, 检, 鑒
  • 查, 察 (with 检查 =~ 监察)
  • 接, 结, 节 (bamboo section between two nodes: period), 季, 期, 纪, 届, 阶, 句
  • 连, 联 (with 连接 = 联结)
  • 受, 收 (with 接收 =~ 接受)
  • 克, 可
  • 共, 公
  • 作, 做, 措
  • 错, 蹉
  • 必, 逼
  • 需,须 (with 需要 =~ 须要)
  • 寻, 询, 讯, 巡
  • 理, 礼, 例 (order, rite, rule)
  • 业, 艺, 役
  • 训, 驯, 巽
  • 符, 复 (assignment symbol)
  • 熔,融
  • 割,革 (cut, skin off)
  • 进, 晋
  • 娱, 愉
  • 告, 造, 叫

We can sum up all the options into this decision tree:

"Keyed" indicates the addition of semantic keys, whereas "complex" means that several sinograms are combined with a situation relationship.

“Modified" indicates that 转注字 are obtained by graphical modification of a common ancestral sinogram, whereas in my proposed 只声转注字 there is no graphical connection, only sound and sense.

"Direct" indicates that 假借字 takes the target ideogram without modification, which forces of the original usurped meaning to form a new 变意字 to be written.