How can I make it stay daytime all the time?

The only ways I can think of involve using game commands.

One way is to get into the console and type /gamerule doDaylightCycle false

Alternatively, you can use a combination of Daylight Sensors and Command Blocks to execute the command /time set 1000. The downside to using this is that you need to stay within range to keep the area around the command block loaded. Running across the world allows night to come again.

Here's an tutorial video that explains how to set up the Daylight Sensor method:
How to make it always day or night in Minecraft using Command Blocks and Daylight Sensors

All you have to do is: use a command block, some redstone, a redstone torch, and a daytime sensor.

1. input /time set day into the command block.
2. place down the daylight sensor.
3. place down a redstone torch.
4. connect the redstone from the redstone torch to the command block making it to where the torch will send a signal to the command block.
5. connect redstone from the daytime sensor to the redstone torch, making sure the redstone is going from the daylight sensor to the torch to the command block.
6. make sure the redstone torch signal in not going into the daylight sensor, but is going into the command block.

If you follow these easy steps, Minecraft should reset itself to day every time it turns to night. Oh! One more thing; make sure the daylight sensor is outside, if it's not it wont work.

You have to have cheats on.

Answer 1. The best way to do it is use the command /gamerule doDaylightCycle false.

Answer 2. Materials you need: 1 Command Block, 2 Blocks, 4 redstone, 1 redstone torch and 1 daylight sensor. NOTE: this is the most compact way I can think of doing it.

Step 1: Place command block and place 2 redstone running into it.

Step 2: Place a redstone torch ON A BLOCK to the side of it (so the block is touching the line of redstone).

Step 3: Place a block ONTOP of the redstone closest to the command block.

Step 4: Place a piece of redstone ontop of the block with the redstone torch on it and another to the SIDE of it (so the redstone isn't next to the command block).

Step 5 (Last step): Place a daylight sensor next to the redstone, and in the command block type in the commmand "time set day".