Spanish Intro:

Why bother learning Spanish? 
The most spoken language in the world is Mandarin Chinese. This is followed by English and then Spanish. If you know English and Spanish you will be able to speak to more than half the population of the world. In addition it will become handy for when you travel to Europe's most popular holiday destination!
 

What does a Spanish sentence look like?
This is a vast simplification but I will attempt to show you the principal difference between a Spanish and an English sentence from a beginners point of view. First let's look at how we form an English sentence. If you have not learned another Latin language the principal thing that you will find difficult in Spanish, is that the object can come before the verb. See tables:
 

The first thing that you will notice is that it appears that there is no subject. This is because the subject is contained in the verb.
In Spanish ("amo = I love") and the subject pronouns are only used when you really want to emphasize the subject. For example if you want to say "I am English" you would say "Soy inglés" You wouldn't normally say "Yo soy inglés"

When first learning Spanish one of the most difficult things to get used to is that the object can come before the verb. As you can see in the example in the table, the word order for "I love you" would be "you I love" The sooner you get used to this the better.

Generally speaking the word order of an English sentence is more rigid than a Spanish sentence.

What do Spanish verbs look like? 

There are three types of regular verbs in Spanish. Those that end in  -AR, -ER and -IR.
Spanish has an inflexional verb system which means that each verb has a root and an inflexion. The root tells you which verb you are using and the inflection tells you the tense (time) and which person you are referring to. The sooner you learn the most common inflections the better, here is an example for the verb "trabajar":

 

How do I ask a question in Spanish? 
In English we change the order of the subject and person in order to make a question:
(affirmative) = They have eaten
(interogative) = Have they eaten?

In Spanish there is no change in the word order.  You know that someone is asking a question because there is a change in intonation at the end of the sentence.  In written Spanish there are question marks both at the beginning and at the end of the question:  ¿Tienes fuego? (Do you have a light?)

There is also another way to make a question. In English it is called a tag question. eg. You live in Spain, don't you?
This is a difficult system for foreigners learning English but in Spanish it is very easy. You just add "verdad" or "no" to the end of the question and use a question intonation. For example:
¿Vives en España, verdad? or  ¿Vives en España, no?
Note ("verdad" means "True")
If you speak Spanish a lot you may find yourself using ¿no? when you go back to English.

How do I make negative sentences in Spanish? 
This is very easy you just put "no" before the verb.
No vivo en Paris.  = I don't live in Paris.

How do I use adjectives in Spanish? 
As in most Latin languages the adjective goes after the noun. In English it is the opposite: In English we say: "A red book" but in Spanish we say "A book red"
Eg. A red book = Un libro rojo.

All nouns in Spanish are either masculine or feminine and when we use an adjective they must agree with the gender of the noun. Also the adjective must agree in number so if the noun is plural so is the adjective.
Generally speaking masculine adjectives end in "o" and feminine adjectives end in "a". There are also a lot of adjectives that do not have an "a" or "o" ending eg. verde=green in which case there is no difference when you use them with masculine or feminine nouns.
 

By the way some of them are not regular, i.e. do not follow the above rules. Here are some very common ones:

la mano = hand -  la foto= photo -  el día = day - el mapa = map - el programa = program - el sistema = system - el problema = problem -el clima = climate

4. Spanish has an informal and a formal form of address, i.e,  "What is your name?" can be:
Formal: ¿Cómo se llama usted?
Informal: ¿Cómo te llamas?
Literally translated. - "What do you call yourself?".
It is very difficult to know which one to use and there are different social norms especially in South America. The formal form is becoming less used. If you ask a Spanish person to explain it to you each person will give you a different answer. I personally only use "usted" if I am speaking to someone I do not know and it’s in a formal situation, i.e business, or the situation demands formality, i.e, a much older person, a person we have just met in a formal environment. Normally it is a combination of both the environment and who you are speaking to. By the way did you know that a formal and an informal form of address used to exist in English?  (hence the use of "thou", "thee", "thy", "thine", and "ye") .

5. The big problem with learning any language is understanding what people say when they are speaking fast.

What are the easiest things about learning Spanish for an English speaker? 

1.In English there are 13 vowel sounds in Spanish there are only five (aeiou) Spanish is a syllable-timed language so the vowels stay the same length no matter where they are in a sentence. Imagine how difficult it is for a learner of English when most English words have a long and a short form or a strong and a weak form. Look at the sentence: "Do you think John would like to go for a drink?" In English this could be pronounced "De yu think John ud like tu go fe u drink?" This problem normally doesn't exist in Spanish because all the vowels are fully pronounced. Sometimes in regional accents some of the consonants are dropped for example in Andalucía they drop the final "s" from most words.  The is also a widespread silent consonant in the past participles eg. "hablado" = spoken.  Sometimes the Spanish do not pronounce the "ado" so "hablado" would be said as "hablao".  So Spanish pronunciation is quite easy to learn although it is difficult to speak without a foreign accent. Maybe, some good advice would be to learn the vowel sounds and then pronounce everything. If you have Spanish friends who speak a little English you may notice that they tend to over-pronounce.
By the way, the Spanish word which contains all the vowel sounds is "murciélago", which means bat (the one that flies not the baseball type).

2. It is very easy to write in Spanish. Once you have learned which sound corresponds to each letter you can easily write correctly in Spanish. The only difficult thing with writing is the accents.

3. It is easy to make affirmative, negatives and questions.

4.  Just open any dictionary and you will find that 50% of the words are very similar.

 Credits to John and Sarah,  from Lingolex. I edited some of the content.