The best way to learn any language is by immersion in an associated culture. Surrounding yourself with native speakers will increase your proficiency much quicker than being in the classroom. With this in mind, many students of Spanish travel to Spanish-speaking countries to gain that all important first-hand experience.
However, much like British English and American English, there are different varieties of Spanish on either side of the Atlantic. Most language schools in London, and elsewhere in the UK, teach Spanish Spanish – the language of Spain. If you are travelling to Mexico (home to the largest Spanish-speaking population in the world), it is important to be aware of variations in the language to avoid miscommunication.
Pronunciation
Mexican and Spanish speakers are able to communicate despite phonetic differences. A student of Spanish who travels to Mexico is unlikely to have difficulties being understood by Mexican Spanish speakers. However, there are differences in pronunciation to watch out for.
In Spain, for example, l and r ending words are often more differentiated than in Mexican Spanish. In Mexico the seseo is a common feature. This means that a voiceless s is used in words where European Spanish speakers typically use ‘th’. This produces homonyms in Mexican Spanish such as casa and caza.
Grammatical variation
In Mexican Spanish questions are often formulated with quantifiers. This means that ‘¿Qué tan…?’ is used, whereas in Spain the same question is more likely to be formulated with ‘¿Hay…?’ This corresponds to the difference between the examples ‘How good is your Spanish?’ and ‘Are you good at Spanish?’ 
In addition, the plural second-person pronoun ‘you’ in European Spanish is vosotros, whereas ustedes is commonly used in Mexican Spanish. Many of the Spanish courses London offers will cover basic differences in grammar between varieties of the language. Informal phrases and sayings, however, are often difficult to grasp from textbooks.
Slang and idioms
As with every living language, Spanish is constantly changing. The best way to become familiar with slang terms and informal expressions is to interact with native speakers. This does not mean the learning process is entirely trial and error, as there are some common phrases you can learn before travelling overseas.
In Mexican Spanish the informal greeting ‘¡Qué onda!’ is common, being the equivalent of ‘What’s up?’ The exclamation ‘How cool!’ is ‘¡Qué chido!’, and ‘Did you get it?’ is ¿Ya te cayó el veinte?’ (Literally: ‘Has your twenty fallen?’)
A buena onda is a ‘good vibe’ while some speakers will receive a shock with ‘¡híjole!’ A Spanish dictionary will inform you that lana translates to ‘wool’; however, in Mexican Spanish it is also a slang term for money.
Some Mexican slang terms can cause offence, but others have evolved from insults to terms of endearment. It is not unusual to call a friend ‘guey’, or ‘buey’, which translates to ‘ox’. However, it now has the same meaning as ‘dude’ and is a term suggesting friendly banter. Of course, when learning Spanish, the Mexican saying ‘Echando a perder se aprende’ is sound advice: ‘We learn best through experience.’