Step 1: What You Need
-Small on/off switch, either push button or toggle switch
-3 AA or AAA battery holder or 3.5 Volt DC power supply
-Solder and soldering iron/gun
-Dremel or other grinding tool
-Hot glue gun
Step 2: Grind The LEDs
The reasons for grinding the LEDs is both to make them lower profile, and also to frost the top surface so that the light output is diffused.
After grinding bend all the wires 90 degrees at the base of the LEDs. Bend all the wires the same way - polarity matters on LEDs. This will allow all the LEDs to be soldered together into one chain.
Step 3: Solder The LEDs Together
After soldering, check if the chain is straight - resolder the crooked links until the LEDs form a straight line.
Test the string with some button cell batteries or with the 3 AA/AAA battery pack.
Step 4: Add The Switch And Power Supply
Solder the wires to the LEDs. Solder the negative wire straight to the battery pack or power supply and solder the positive wires to the power switch.