Putting Character Codes to Work

This goes well beyond the above tip, but shows how to use the simple approach of holding down the Alt key and using the numeric keypad for many of the Unicode characters.
Additionally, there is a simple technique for typing Unicode values with the regular keyboard to produce the corresponding symbols. Finally, you can select and copy characters from the Character Map applet available in all versions of Windows for decades.

Suppose that you want to use an Infinity symbol. It is available in Arial, Calibri, Tahoma, Times New Roman, and MANY other fonts.

Technique 1. This requires some upfront work, but it can save a huge amount of time and effort later, and it's also an educational experience.
In its lower-left corner, Character Map displays the hexadecimal Unicode value and the name of any selected character. The character for Infinity shows U+221E. But that is a hexadecimal value. You need the decimal equivalent, which is 8734. So, hold down the Alt key, on the numerical keypad, type 8734, and release the Alt key. The Infinity character appears. Very easy!
The hard parts are finding the hexadecimal value and the decimal value, which you can do with Character Map and a good calculator. Or better and easier, for a limited set of values that you use often, you can create an Excel spreadsheet to make and print an easy "cheat sheet" that shows the decimal values. In one column, place the names (or copy the symbols from Word) that you use often; in the next column, place the corresponding hex values as four digits that you find in Character Map (you'll see many interesting characters), and in the next column use the formula =HEX2DEC(number). So, if cell A5 contains the name Infinity, and cell B5 contains 221E, place =HEX2DEC(B5) in cell C5. It will show 8734. Copy that formula to all the cells that need a value in the C column, and you can print your cheat sheet. Refer to the sheet to type your favorite symbols with ALT+[4 characters].
(see Figure 1 below)

Technique 2. This requires that you know the hexadecimal code for the character that you want. You can find it in Character Map. Type the hex code with your regular keyboard keys. To get the Infinity character, type its code, 221E. Then select that four-character code and press ALT+X. That is, hold down the Alt key, press and release X, and release the Alt key. The Infinity character appears. That's a toggle. You can press Alt+X again to get back the221E.
Suppose you found a symbol you might want on an internet page. You can copy and paste, for example, a Less-Than Or Equal To character. Select that character that was pasted into your document, and press Alt+X to see its code, 2264. But maybe what you needed was the Greater-Than Or Equal To character, which you couldn't find easily. Many related characters have similar codes. You have 2264. Change the 4 to 5, select the 2265, and try Alt+X. There it is.
But after a while, you'll probably decide it's easier to create a cheat sheet as in Technique 1.
(see Figure 2 below)

Technique 3. This is most useful for rarely used special characters, such as those in the Webdings or Wingdings fonts. In Character Map, find the character that you want; such as the Wingdings clockface showing 3 o'clock. Click that character, and then click the Select button. (You can select multiple characters this way.) It appears/they appear in the Characters to copy box. Select (highlight) the characters in the box that you want to copy, and then click the Copy button.
Paste the characters into Word.