Learn Hardcore Indonesian: Guru kami sangat ramah.

Guru kami sangat ramah. = Our teacher is very friendly.
Dia pintar. = He/She is smart. Avoid using adalah before an adjective (see a later question for details).

What’s the difference between kami and kita? Which one fits here?

kami = we/us (excluding the person you’re talking to)
kita = we/us (including the person you’re talking to) Use kami if the listener is not part of your group. If you’re speaking to a classmate who shares the teacher with you, say: Guru kita sangat ramah.

Does guru kami mean one teacher or more than one?

Indonesian nouns don’t change for number. Guru kami can mean our teacher or our teachers, depending on context. To make it clearly plural:

Guru-guru kami sangat ramah. (neutral)
Para guru kami sangat ramah. (more formal) To say one of our teachers:
Salah satu guru kami sangat ramah.

Where should intensifiers go? Can I use sangat, sekali, or banget?

sangat (very) goes before the adjective: sangat ramah.
sekali (very) goes after: ramah sekali.
banget (very, colloquial) also goes after: ramah banget (informal). Examples:
Guru kami sangat ramah.
Guru kami ramah sekali.
Guru kami ramah banget. (casual) Related words: amat (very, formal), terlalu (too), cukup (quite), agak (rather).

Can I say Guru kami adalah sangat ramah?

No. adalah is not used before adjectives. Use:

Guru kami sangat ramah. Use adalah when the predicate is a noun (especially in formal writing):
Guru kami adalah panutan. (Our teacher is a role model)

Can I drop kami and just say Guru sangat ramah?

You can, but it becomes vague: it could mean the teacher is very friendly, a teacher is very friendly, or teachers are very friendly—context decides. To be specific:

Guru itu sangat ramah. (that/the teacher is very friendly)
Guru kami sangat ramah. (our teacher is very friendly)

How do I negate it? How do I say Our teacher is not very friendly?

Use tidak to negate adjectives. For not very, use tidak terlalu or kurang.

Guru kami tidak ramah. (not friendly)
Guru kami tidak terlalu ramah. (not very friendly)
Guru kami kurang ramah. (somewhat unfriendly/less friendly)

What’s the difference between ramah and ramai? They look similar.

ramah = friendly, pleasant in manner.
ramai = crowded/noisy/bustling. Examples:
Guru kami ramah. (friendly)
Kelas kami ramai. (the class is crowded/noisy)

Is ramah the same as baik?

Not exactly.

ramah = friendly, warm, approachable.
baik = good, kind, well-behaved; also used to say OK when agreeing. Examples:
Dia ramah kepada semua orang. (friendly to everyone)
Dia orang yang baik. (a good/kind person)

How do I politely refer to a teacher? Should I add Pak or Bu?

Yes, use:

Pak (Mr./Sir) for men; Bu (Ms./Ma’am) for women. Examples:
Guru kami, Bu Sari, sangat ramah.
Addressing a teacher: Pak/Bu, or Pak Guru/Bu Guru in schools.

Can I use guruku or gurumu? How do these compare to guru kami?

guruku = my teacher (guru saya)
gurumu = your teacher (guru kamu/Anda)
gurunya = his/her teacher, or the teacher (previously mentioned) There is no suffix for our. For our teacher, use the full pronoun:
guru kami (excluding the listener)
guru kita (including the listener)

How do I turn it into a noun phrase like a very friendly teacher?

Inside a noun phrase, put the adjective after the noun, and use yang if you add an intensifier:

guru yang sangat ramah = a very friendly teacher
guru ramah = a friendly teacher (no extra emphasis) The sentence Guru kami sangat ramah is a full clause, not a noun phrase.

Can I front the adjective for emphasis, like Very friendly, our teacher?

Yes, for emphasis or a literary feel you can front the predicate:

Sangat ramah guru kami. This is stylistic; the neutral everyday order is Guru kami sangat ramah.

Do I need a word for the in Indonesian? How do I say the/that teacher?

Indonesian has no articles. Use demonstratives to specify:

ini = this, itu = that. Examples:
Guru ini sangat ramah. (this teacher is very friendly)
Guru kami itu sangat ramah. (that/aforementioned our teacher is very friendly)

Does ramah appear in other common expressions?

Yes:

ramah tamah = sociable/cordial (as a noun or descriptor)
ramah lingkungan = environmentally friendly
keramahan = friendliness
keramahtamahan = hospitality