Here's a mistake to avoid.
 
If you've learned some Spanish you probably know that the translation of the word "of" is de and the word "about" can be acerca de or sobre.
 
When you're dating someone it's popular to tell them that you've been thinking "about" or "of" them.
 
I've been thinking about you.
 
I always think about you.
 
I think about you all the time.
 
In Spanish when it comes to "thinking about you" or "thinking of you" the literal translation isn't used. Instead of translating the word "about" or "of" the word en is used. En means "in" or "on" but in these examples it's the correct translation.
 
So:
 
I've been thinking about you.
He estado pensando en ti.
eh ehs-tah-doh pehn-sahn-doh ehn tee.
 
I always think about you.
Siempre pienso en ti.
see-ehm-preh pee-ehn-soh ehn tee.
 
I think about you all the time.
Pienso en ti todo el tiempo.
pee-ehn-soh ehn tee toh-doh ehl tee-ehm-poh.

There are two ways to say "I miss you" in Spanish that are the most common. Which one you will hear more depends whether you are in Spain or Latin America.

The most common way to say "I miss you" in Latin America uses the verb extrañar:

I miss you.
Te extraño.
teh ehks-trahn-yoh.

The most common way to say "I miss you" in Spain uses the verb echar:

I miss you.
Te echo de menos.
teh eh-choh deh meh-nohs.

Here are two more ways to say it that aren't as common as the above phrases:

I miss you. / I need you.
Me haces falta.
meh ah-sehs fahl-tah.

The literal translation of the above phrase doesn't translate very well to English. It uses the word falta which means "lack." It translates more to "I need you" but it is commonly used to say "I miss you" and means basically the same thing.

Here is another way to say "I miss you":

I miss you. / I long for you.
Te añoro.
teh ahn-yoh-roh.

The above phrase is not very common but says "I miss you" with a little more flair. It's like saying "I long for you."

I'll mention a couple mistakes to watch out for.  

Remember if you are talking about “missing” a bus or plane because you did not make it on time use the verb perder instead of the above verbs:

I missed the plane because I woke up late.
Perdí el avión porque yo me desperté tarde.
Pehr-DEE ehl ah-vee-OHN pohr-keh meh dehs-pehr-TEH tahr-deh.

If you want to say you “missed out” on some event like a party or soccer game you can use the reflexive version of perder which is perderse:

I missed out on the party.
Me perdí la fiesta.
Meh pehr-DEE lah fee-esh-tah.

Spanish has a few different ways to say you like someone. The two most common verbs for liking someone are gustar and caer. When gustar is used in reference to a particular person it has sexual connotations. It means you like this person in a romantic/sexual way. Caer has no sexual connotations. It means you like this individual as a person.

When using gustar and caer also note that unlike English the person you say that you like is the person creating the action of the verb. In English when you say “I like this person," you are the one creating the action, “the liking.”

With gustar and caer the person you like is the one creating the verb action. Instead of saying ”I like this person” it’s more like saying “This person pleases me.” The other person is creating the action of the verb.

Here’s how to tell someone you like them using both gustar and caer:

I like you. (in a romantic/sexual way)
Me gustas.
meh gooss-tahs.

I like you. (as a person, no romantic/sexual connotations)
Me caes bien.
meh kah-ehs bee-ehn.

Using caer requires an adjective to express whether your opinion of this person is good or bad. The adjective bien in the example above means “fine” or “well.” By changing the adjective to a negative word like mal which means “bad” or “badly” you change it to “I don’t like you.”

I don’t like you.
Me caes mal.
meh kah-ehs mahl.

If you have any tips or something to add related to this post just mention it below.

When people are learning Spanish and want to ask someone if they have a boyfriend or a girlfriend they normally translate it literally from English.
 
In English we say "Do you have a boyfriend (or girlfriend)?"
 
The problem is in Spanish they don't use the indefinite article (the "a" that comes before "boyfriend" or "girlfriend.")
 
In Spanish they just say "Do you have boyfriend?" or "Do you have girlfriend?"
 
So here are the correct translations:

Do you have a boyfriend?
¿Tienes novio? (The indefinite article "un" is not used before "novio.")
Phonetics:
¿tee-ehn-ehs noh-vee-oh?
 
Do you have a girlfriend?
¿Tienes novia? (The indefinite article "una" is not used before "novia.")
Phonetics:
¿tee-ehn-ehs noh-vee-ah?
 
Here's how to respond if someone asks you:
 
I (don't) have a boyfriend.
(No) tengo novio. (No "un" is used. Don't say "Tengo un novio.")
Phonetics:
(noh) tehn-goh noh-vee-oh.
 
I (don't) have a girlfriend.
(No) tengo novia. (No "una" is used. Don't say "Tengo una novia.")
Phonetics:
(noh) tehn-goh noh-vee-ah.

By using the words in parenthesis you negate the sentence and state you don't have a boyfriend or girlfriend.

If you have any tips or something to add related to this post just mention it below.