Talk to people about English
This is a very simple method, but it is very effective. Here's how it works:

You usually talk about things which interest you. But the opposite is true, too. If you start talking about a boring subject, you will begin to get interested in it.

Imagine you are studying a subject that you hate. You are bored and tired, but you have to pass the test tomorrow. If there are people near you, you have two options: you can tell everybody how much you are suffering or you can tell those people about the things you've learned. If you choose the first option, you will only feel worse.

If you choose the second option, and start a conversation on the "boring" subject, you will begin to look at it in a totally different way. Suddenly it will become a subject worth talking about — therefore, an interesting subject.

How can you begin such a conversation? If you're studying English, you can surprise another person by talking to him/her in English. Say (in English): Hi, I'm studying English and I hate it. Or you can say (in your first language): Hey, I've learned 50 English words today. Do you know what's the English word for ...? If there are no people near you, you can telephone or send an e-mail message to your friend.

What will your friends say? Probably they won't be very interested, but it doesn't matter! The important thing is this: After talking about English, you will study it with much more passion. Try it.

Find a friend who is learning English
If you can find a friend who is learning English and is on a similar level of skill, you will be in an excellent situation:

you will have someone to talk about English with. These conversations will increase your interest in English, as explained in the previous section.
learning English will be easier, because you will be able to discuss your problems with your friend.
you will study English more, because you will want to be better than your friend. :-)
You should meet your friend regularly. Ideally, he/she should live near you, or go to the same school as you. If you absolutely can't find anybody willing to learn English with you, you can try to find somebody by e-mail. This is a worse solution: your conversations will probably be less frequent, and it is difficult to compete with someone who you don't know well.

Spend some money on learning English
If you spend your money on something, you will want to use it. For example, if you buy an expensive tennis racket, you will probably go out and play tennis every day.

This rule is also true for learning English. If you want to increase your desire to learn English, buy a new dictionary, a new SuperMemo collection, an interesting English-language book, English-language cable TV, etc. The idea is simple: You paid for it, so you will want to use it, and you will improve your English.