I'm disheartened by the trend towards tea over the last few years. The solid kick in the pants that a cup of coffee brings is something I'm reluctant to live without.
First of all: Get loose leaf black tea, trying out several varieties to find a baseline one you like. Black tea is the simplest to brew of all the caffeinated tea variants. You'll also want to experiment with water temperature, steeping time (not that long, else you'll get the bitter flavor bits that no one like), and how you go about steeping (i 've found that disposable tea bags that I can fill with loose tea is best for me). I've fine tuned this process for myself to the point that I can make super strong tea that also naturally tastes sweet!
The mistake that many people make with tea vs coffee is that they equate the jitteriness with the caffeine working. In tea, there is also theanine, which moderates the jitters that occur due to caffeine via being a very mild muscle relaxant, and I am lead to believe that theanine has been found to have wholely positive cognitive effects generally.
That being said, coffee or tea are only helpful if you have a caffeine dependency, or you are amidst being tired/groggy to an extent that interferes with work. If your issues with doing work are not those, drink the tea anyways because its tasty, healthy and easier on the stomach/body than equivalent volumes of coffee (also tasty) or sugary(real or fake) energy drinks. and/or go talk with a doctor to figure out why you can't do work.
As a tip to those who might want to give tea a try, the pattern of increased bitterness with increased steeping time is highly dependent on tea quality. Not necessarily price, but quality.
Don't be afraid to do some research, talk to local tea lovers, etc. to find the best quality (not simply the most expensive, as that is a sure way to just get ripped off) loose tea in your area. You'll be rewarded for it in terms of the freedom you have in steeping time, as better tea can be steeped longer and to stronger flavour without developing bitterness. (Higher-quality tea can also be reused for another steeping or two (gasp!) and still deliver great flavour, making it an even better value.)
For those coming off of a strong coffee habit, you can have yourself a nice, strong (but almost never bitter!) replacement in no time.