Many people have trouble adding description to their games. They have heard all the "use five senses rules" and "add a bit of description to every mechanic" advice, but it is not cutting it for them. Those pieces of advice are good, for as far as they go. What you need is concrete advice and specific tools on how to do this.
There are two simple tools you can use to increase your level of description and your skills at producing it.
The main tool is the cue card. Taken from its television roots, the cue card is a note card that tells you what to say in a given situation. Usable by GMs or players, the cue card provide "notes" on things. When in the appropriate situation, you pull it out, rattle off the description/ dialog/ action, and move on.
When a GM, I use cue cards for settings (specific places or generic street/ wilderness/ etc), weather (a few cards for each season or weather type), bits of dialog (one liners or key phrases), bits of action description (describing tactical actions or how certain things are done), or other descriptions that can be quickly added to any action. Any related game mechanics are usually included on the card. Cue cards are traditionally made on 3x5 cards, but they can be typed out on sheets, or any medium that is useful to you. The advantage of cue cards is that if you have a great idea on how to play your character while not playing, you write it down and can use it for later.
An aside: To keep the description consistent for the entire campaign, I base my words and phrases on a favorite author. One author forms the inspiration and the template for the voice of the campaign. Right before the game, I'll read a chapter or large chunk of one author, Mercedes Lackey, Ann Rice, Terry Brooks, Peter David, or some such, so that I have an idea of how the author would describe the scene. It reinforces the "voice" of the campaign in my mind.
Filling up cue cards is not a monolithic task. Start small. Do a few every now and again. Eventually you will find yourself with more cards than you can conviently carry.
Where do you get the info to fill a card is the question I am hearing from you now. There are two methods. The first is to borrow a descriptive bit from your campaign's author. The second, and by far the most common, is Riffing. This is the second tool.
Riff on important or notable non player characters when you have free time. When you're in the car or shopping or in the shower (or any place your mind can safely waunder), think of situations your NPC might be in, and how they'd react. Think about the dialog, the feelings, the actions, and the responses of others in that situation. These riffs will help you better define the NPC and give you "prepared" responses. Write down any important bits you discover on a cue card.
I also riff on possible combat actions. I see a cool martial manuver in a movie or read slashing fight scene in a book, these things see with me. If I riff on a fight scene, I can write what I see in my mind the character (or type of character/ monster) doing. It is sort of a mini-movie of an action scene. I adapt what I see into a brief bit of description, and write down the appropriate mechanics. If it is for a specific character, I actually write down the numbers to roll against. (I have a dozen or so cards for Zombies shuffling, lunging, lurching, grasping with cold, claylike hands... etc)
Scene Riffs are very possible. Locations are characters that don't have arms, legs, and mouths. Think about various areas of your campaign setting when you have free time, such as when you're in the car or shopping or in the shower. There are various ways to describe any place, each one conveying a different feeling or view of the world. (Hmm is this a normal alley, a dark and evil alley, a place where the homeless go, or what?) These places will be with you when you need to describe a place while playing.
Note: Credit goes to Jonathan Winters, who created this tip of riffing or working things out ahead of time for improvisational comedians. So they will be there when the comedian needs them.
These two tools will increase your descriptive powers. They discipline you to work on them. They help you hone your craft and increase your arsenal of descriptive tools. These are not just "an idea to try out", but solid tools that are useful.
PS: After a while, once you get into the habit of riffing and cue carding, you will no longer have to use cue cards. You will have all your cards memorized and ready at the tip of your tongue. However, this usually happen after you have a huge number of cards and an organizational system to keep tracking of them.
Oh one more thing. Players can use cue cards and riffing too. Players should riff on their character or a character they might want to play when they have free time. When they're in the car or shopping or in the shower, they can think of situations the character might be in. Determine what they would do in the situation. They can think about the dialog, the feelings, the actions, and the responses towards others in that situation. These riffs will help them better define their characters and give them "prepared" responses. They too must write down any important bits they discover (see cue cards). If any game mechanics might be involved, they might want to "freshen up" their knowledge of the applicable game mechanics. When they do, they manage to improve their own part of the narrative, inspiring the rest of the troupe to new heights.
Some links that might be useful for you. These are specific searches on www.openroleplaying.org
where I have posted 1200+ game related tips. Acting Presentation ToolsCharacter Development Riffs/ Ideas
You can find other useful ones as well. Either do the zen search and press refresh f5 alot or a key word search. Once you find a tip title that interests you, search on it and see the rest of series on that subject.