Antes de entrar en mi cuarto, suelo descalzarme y dejar los zapatos junto al mueble de la entrada.

Because after antes, Spanish normally uses de + infinitive when the subject stays the same.

• Antes de entrar... = Before entering... / Before I enter...
• Después de comer = After eating
• Antes de salir = Before leaving

If the subject changes, Spanish usually switches to a full clause:

• Antes de que entres... = Before you come in...

So in your sentence, antes de entrar en mi cuarto is the standard structure.

With entrar, Spanish often uses en to show the place you are entering, especially in standard Peninsular Spanish.

• entrar en casa
• entrar en la habitación
• entrar en mi cuarto

In some varieties of Spanish, especially in much of Latin America, you may also hear entrar a:

• entrar a mi cuarto

For Spain, entrar en is very natural and standard.

Yes, suelo can mean floor, but here it is the 1st person singular form of the verb soler.

• suelo = I usually / I tend to
• el suelo = the floor

So:

• suelo descalzarme = I usually take off my shoes

The meaning is clear from the grammar. Since it is followed by an infinitive, it must be the verb soler, not the noun suelo.

Soler is used to talk about habits or things that happen regularly. It is normally followed by an infinitive.

• Suelo leer por la noche = I usually read at night
• Sueles llegar tarde = You usually arrive late

In your sentence:

• suelo descalzarme y dejar... = I usually take off my shoes and leave...

A useful thing to know: soler is not used in all tenses as freely as normal verbs. You will most often see it in the present and imperfect:

• suelo = I usually do
• solía = I used to do

Descalzarse means to take off one’s shoes / to remove footwear.

So:

• me descalzo = I take my shoes off
• suelo descalzarme = I usually take my shoes off

It is a very natural verb here. Another common way to say the same idea is:

• quitarse los zapatos

So both of these are possible:

• Suelo descalzarme
• Suelo quitarme los zapatos

The first is a bit more compact because the verb itself already contains the idea of removing footwear.

Because descalzarse is used reflexively when the person removes their own shoes.

• descalzar = to remove shoes from someone or something
• descalzarse = to take off one’s own shoes

The me shows that the action happens to the speaker:

• descalzarme = to take off my shoes
• descalzarte = to take off your shoes
• descalzarse = to take off his/her/their shoes

After a conjugated verb plus infinitive, Spanish lets you place the pronoun in two ways:

• suelo descalzarme
• me suelo descalzar

Both are correct. In your sentence, attaching it to the infinitive is very natural.

Because one soler can govern two coordinated infinitives.

• suelo descalzarme y dejar los zapatos...

This means:

• I usually take off my shoes and leave the shoes...

Spanish does not need to repeat suelo before the second infinitive unless you want extra emphasis, and even then it would usually sound unnecessary.

This is very common:

• Suelo cocinar y escuchar música
• Suelo levantarme, ducharme y salir temprano

Because in Spanish, when ownership is obvious from the context, the definite article is often used instead of the possessive.

Here, since the speaker has just said descalzarme, it is already obvious that the shoes are theirs.

So Spanish naturally says:

• descalzarme y dejar los zapatos

rather than necessarily:

• descalzarme y dejar mis zapatos

Using mis zapatos is not wrong, but it adds emphasis, contrast, or explicitness that is not really needed here.

This is very common in Spanish:

• Me lavo las manos = I wash my hands
• Me pongo la chaqueta = I put on my jacket

Junto a means next to, beside, or by.

So:

• junto al mueble = next to the piece of furniture

The al is a contraction of:

• a + el = al

So:

• junto a el mueble → junto al mueble

That contraction is required in normal Spanish.

A similar phrase is al lado de, which also means next to:

• junto al mueble
• al lado del mueble

Both are natural, though junto a can sound a bit more compact or slightly more formal in some contexts.

Here la entrada means the entrance area, entryway, or hall of the home, not the act of entering.

So el mueble de la entrada means something like:

• the piece of furniture in the entrance hall
• the hall table / entryway furniture

Spanish uses mueble very generally for piece of furniture, so it does not tell you exactly what kind of furniture it is. It could be a small table, cabinet, shoe unit, etc.

In a home context in Spain, la entrada very naturally refers to the space just inside the front door.

Cuarto can mean room, and depending on context it can also imply bedroom.

In this sentence, mi cuarto will often be understood as my room, and in many contexts that means my bedroom.

Related words:

• cuarto = room; often informal and common
• habitación = room; more neutral/general
• dormitorio = bedroom specifically

So:

• mi cuarto = my room
• mi habitación = my room
• mi dormitorio = my bedroom

In everyday Spanish in Spain, cuarto is very common.

Yes, you may hear that, and it is widely understood. But for Spanish from Spain, entrar en mi cuarto is more standard and natural.

So for a learner focusing on Spain:

• Prefer entrar en mi cuarto

If you later hear:

• entrar a mi cuarto

that is not something to be surprised by; it is just a variation that is especially common in many Latin American varieties.

Yes, but in this kind of sentence dejar often means to leave in the sense of to put or to leave something in a place.

So:

• dejar los zapatos junto al mueble = leave / put the shoes next to the furniture

It does not mean leave behind forever. It simply means placing them there.

This is a very common use of dejar:

• Dejé las llaves en la mesa = I left the keys on the table
• Deja la chaqueta aquí = Leave/put the jacket here

Because that opening phrase is an introductory time expression, and Spanish often separates that kind of phrase with a comma for clarity.

• Antes de entrar en mi cuarto, suelo...

The comma helps mark the pause before the main clause.

In short sentences, punctuation can sometimes vary, but here the comma is completely natural and helps the sentence read smoothly.

Yes, it sounds very natural for Spain.

A few details that fit well with Peninsular Spanish are:

• entrar en rather than entrar a
• cuarto as a normal everyday word for room
• the overall rhythm and vocabulary of the sentence

Nothing in it sounds unusual or forced. It is a very believable everyday sentence in Spanish from Spain.