Contrary to hieratic and demotic, which were only written from right to left, hieroglyphs could be written from right to left or from left to right. Both hieroglyphic and early hieratic could be written in lines or in columns, but as it evolved, hieratic would be restricted to lines whereas hieroglyphic continued to be written in lines and columns.

Finding the start of the text is fairly easy. Signs that represent humans or animals look towards the beginning of the text. If, for example, the signs look to the left, then the text is read from left to right. Hieroglyphs are (almost) always written from top to bottom. Even when they are arranged in lines will one read a sign that is directly above another before reading the one below.
 

Interactive example showing the same text 4 times, each with a different orientation.
Moving the mouse over any part of the text will reveal in which direction it is to be read.

When hieroglyphic text was used as a legend, a comment or as "words spoken by" with an object, a god or a person, the signs would be oriented in the same way as the accompanying image. Thus in a scene where a king makes an offering to a god, the text with the king and his offering is oriented in the same way as the king opposite the text of the god: within one text one can often find hieroglyphs written from right to left as well as from left to right! When a scene has texts that are written in both directions, either text will start somewhere near the middle. Which part of the text is to be read first (if there is such a notion as one part taking precedence over another) must be found examining the texts.
 

Ptolemaios III Euergetes I gives a field to Amun in a ritual scene on the Propylon of the temple of Khonsu at Karnak. The hieroglyphs are oriented in the same direction as the images they are related to.

The need to write hieroglyphs in lines or in columns was more an aesthetic and practical need: the ancient artists had to make optimal use of the space they had for their text and image.

Disposition of the signs

The disposition of some signs could be changed by religious or practical reasons: 

• religious motivations made that signs or words representing holy notions such as the word "god" or the name of a god or goddess, were to be written before other signs. This could influence sign-order, word order and the order of entire parts of sentences. If one wished to write, for instance, "beloved by Amun-Re, lord of the thrones of the Two Lands" one would normally write "Amun-Re, lord of the thrones of the Two Lands, beloved by", and if one wished to write "king of Upper- and Lower-Egypt Menkheperre, beloved by Amun-Re, of the gods king" one would normally write "Amun-Re, king of the gods, king of Upper- and Lower-Egypt Menkheperre, beloved by", ...
• the same applied to words related to the kingship. The word "king" would often be written before other words related to it. Thus palace was written "of the king, house" and prince "of the king, son" where grammatical rules imply that despite the reversed writing, one still read "house of the king" and "son of the king". This reversal of signs and even entire words or phrases is called honorific transposition. 
• the order of sign was changed for aesthetic reasons as well: tall narrow signs were often placed before signs representing a bird, even when they ought to have been placed behind them. Thus de group is read wD and not wDw.The guiding principle here was that the available space had to be used optimally: the surface of unused space was reduced to a minimal.
• the same principle was also used, not in changing the order of certain signs, but also in their disposition. Low, narrow signs were often placed under the chest or behind the head of signs representing a bird. Thus the group , representing the consonants t-w-t was usually written , which takes up considerably less space. The principle whereby signs are grouped as to have as little empty space as possible is called horror vaccui.