Most competitive tests in India contain many vocabulary-based questions. Therefore, a decent command over vocabulary is absolutely essential to good performance in the English part. A standard English dictionary can help you improve your knowledge and skills.
Therefore, a dictionary which contains just the word meanings is of little use. You can use any dictionary as long as it meets these conditions. In fact, there is no bad dictionary except the one which is not used.
Tips
Try to learn at least 20 news words daily. While reading something, it is desirable to have three things - a dictionary, pen and diary. If you find a new or difficult word/phrase, it is better NOT to look up the dictionary immediately as it will obstruct the flow. Instead, underline or highlight such words and after finishing the article, look up the dictionary for meanings.
Go back to the lines containing those highlighted words and re-read them for better understanding.
Noting down the meanings and usages in your diary can be a powerful method to retain them in memory. This is the best possible dictionary you will ever have. Revise the diary contents often in a cumulative manner e.g. the third week test should be on the coverage done in the first two weeks and so on. Test yourself frequently to get feedback and positive motivation.
Do NOT stop at the word meanings only as a dictionary is a treasure of priceless knowledge about all aspects of words.
Whether a given word is a noun or adjective or adverb or preposition or some other word form. If you really want to polish your language skills, it is important to learn these differences.
How to pronounce a word. In fact, pronunciation is the first thing with which a word entry in the dictionary begins. You can use the Pronunciation Guide given in the dictionary.\
How and Where to use a word APPROPRIATELY.
How NOT to use a given word. It can also tell you a lot about collocations. Collocation refers to how certain words are used together or form fixed relationships.
For example:
Correct Collocation
scanty rainfall
heavy rain
scenic view
discharged from hospital
answer the doorbell
Wrong Collocation
low rainfall
thick rain
scenic picture
released from hospital
reply the doorbell
Learning collocations is a part of learning the language and a dictionary helps you here. This knowledge can be extremely helpful in Sentence Completion questions, often based on such differences.
Which word to use in a particular situation. For instance, the words ask, enquire and demand may look similar meaning-wise but each one has a specific usage. Though all these men to say something to get information, they CANNOT be used synonymously.
Sample sentences:
Ask: Say something as a question to get information e.g. “What are you doing?” He asked me.
Enquire (formal): To ask for information: We called up the airport office to enquire about the next flight.
Demand: Ask a question firmly: “What have you been doing all these days?” she demanded firmly.
The nature and history of words i.e. whether used as slang, abuse, for humour or as a figure of speech, which can help you solve several questions easily. Learning about word origins can help you fix them permanently.
Keep the above tips in mind to make an efficient use of dictionary.