How to make resource pack textures for items?

I'm new to this, so please bear with me. I've been trying to make a resource pack for a map I'm designing. I've been able to change the block textures, but when I try to change an item texture or one of a plant (wheat), it either gives me the pink and black texture error, or an annoying white block around the item. Usually, If I do clinch the texture, the parts I wish to be transparent are not. I've tried several programs for adding transparency, but they've all returned the classic texture error. I'm really confused as to why. Can anyone help me understand, then fix it?

Ok, so this will be pretty hard... anyway so, I'm just gonna tell you what I'd do. So first I'd get a copy of the default Minecraft resource pack. Then when you go into the folder just change the textures and such.

Some warnings: One, Being that some blocks such as grass use special textures, Just drawing all over it will look odd and not look how you want to all the time. (depends on what colour you want it.)

Two, tying to make costume sounds will be very hard. Since 1.7 they changed the way sounds work. However there are ways to fix this, there are some programs that will do this for you. But that is known be a little hard!

Three, When you have finished the resource pack remember to put it into %appdata%/.minecraft/resourcepacks then select it in game. and start game and test it out!

Oh and if you look hard enough you will find every thing you can change, E.g the image that comes up when you put on a pumpkin, or the look of a enchanted item. (the purple flashy bits.)

Hope this helps somewhat, But if it didn't then... i have my excuses, My first post :3 Oh and i was just tying to say everything that might help. since as i don't know how good you are at it at all so i just acted like you needed to know!