Scottish accents vary depending on the section of Scotland a person is from. The west side of the country tends to have a broader accent than the softer-spoken eastern people so before you start learning to imitate a Scottish accent you will need to decide on what type of Scottish accent you will be doing. You can take several steps to improve your Scottish accent, but practice is the key to nailing it.
Determine what type of Scottish accent you will be imitating. People from Edinburgh sound different to people from Glasgow who sound different to people from Dundee. For example, the sentence "I'm going to take the baby to the river for a picnic" might sound like "Ah'm gonny teak the wee bairn te the riv'r f'r a pucnuc" in the east and like "Um gunny tak the wee'un ta the ruvur fe a pucnic" in the west.
Pick out key phrases from the region you are imitating. Scottish people have their own slang, including words such as "wee," "aye," "bonny," "bairn" and "lassie." Bookstores will sell Scottish dialect books so buy one of these to help with your accent. The Internet is also a good source of information on Scottish slang.
Learn to roll your Rs. Scottish people have a tendency to roll this letter when speaking, so practice this technique. Also focus on your vowels. In Scotland the letter "e" is said as though it has been shortened so it is more of an "eh" sound. You can practice both of these by learning to say the word "Scottish." A local person would pronounce this word as "Scoritsh."
Watch Scottish films and TV shows. If you would like to imitate a Glasgow accent for example, study a film or TV program that was made in this area and listen to the voices of the actors. You can also listen to the BBC Scotland radio station online.
Read books written by and about Scottish people. This will help you see the sentence structure and the words that you are learning to pronounce.
If you have the money and the time and you are set on perfectly imitating the Scottish accent, hire a voice coach. This is what actors do when they are preparing for a movie where they must speak in a foreign accent. It will give you the opportunity to be properly taught the speech patterns and language of the Scottish people.