En julio y septiembre me gusta revisar cada diapositiva antes de presentar nada en público.

Because gustar works differently from English to like.

In Spanish, the thing you like is the grammatical subject:

• Me gusta revisar = Reviewing is pleasing to me
• more naturally in English: I like reviewing

So:

• me = to me
• gusta = is pleasing
• revisar = to review / reviewing

That is why Spanish uses me gusta rather than yo gusto in this sentence.

After gustar, Spanish often uses an infinitive to talk about an activity someone likes doing.

Examples:

• Me gusta leer = I like reading
• Me gusta viajar = I like travelling
• Me gusta revisar = I like reviewing

So revisar is not conjugated here because it names the activity itself.

In Spanish, months are usually used without an article after en when you mean in July, in September, etc.

So:

• en julio = in July
• en septiembre = in September

That is the normal pattern.

You may sometimes see articles with months in other structures, but here en julio y septiembre is the standard and natural form.

It means in July and in September specifically.

It refers to those two months as separate times.

If you wanted from July to September, Spanish would usually say:

• de julio a septiembre
• or desde julio hasta septiembre

So this sentence is talking about July and September only, not the whole period in between.

In Spanish, the names of months are normally written in lowercase, unlike in English.

So:

• julio
• septiembre
• lunes
• enero

This is completely standard in Spanish spelling.

Cada diapositiva means each slide or every slide.

Spanish uses cada + singular noun:

• cada diapositiva
• cada día
• cada estudiante

So the noun stays singular after cada.

Compare:

• cada diapositiva = each/every slide
• todas las diapositivas = all the slides

Both are possible in different contexts, but cada diapositiva focuses on the slides one by one.

Here, diapositiva means a slide, especially in a presentation such as PowerPoint or similar software.

In other contexts, diapositiva can also mean a photographic slide, but in this sentence the meaning is clearly presentation slide.

Yes, both can be possible, but they are not exactly the same.

• revisar often means to review, check, inspect, go over carefully
• repasar often means to go over again, revise, rehearse, review for study/practice

In this sentence, revisar cada diapositiva suggests checking each slide carefully before presenting.

If you said repasar cada diapositiva, it might sound more like going over the content again, perhaps to practise or refresh your memory.

So revisar fits well if the idea is checking the slides before speaking in public.

Because antes normally takes de before an infinitive.

So:

• antes de presentar = before presenting
• antes de salir = before leaving
• antes de comer = before eating

This is a very common pattern in Spanish:

• antes de + infinitive

If there is a full clause with a conjugated verb, Spanish often uses:

• antes de que + subjunctive

For example:

• antes de que presentes = before you present

But in your sentence, the infinitive structure is the natural one.

Yes, nada literally means nothing, but after certain expressions it often translates as anything in English.

Here:

• antes de presentar nada en público

means:

• before presenting anything in public

This happens because Spanish often uses nada where English would use anything, especially after words like antes de, sin, or in negative-type contexts.

Compare:

• No veo nada = I don’t see anything
• Sin decir nada = without saying anything
• Antes de hacer nada = before doing anything

So nada is completely natural here.

Because en público is a fixed expression meaning in public.

It refers to doing something openly, in front of other people, not literally being physically inside an audience.

Examples:

• hablar en público = to speak in public
• cantar en público = to sing in public
• presentar en público = to present in public

So en público is the idiomatic choice.

Spanish often leaves out subject pronouns when they are not needed, because the verb form and context already make the meaning clear.

Here, me gusta already tells us the person involved is me / I.

So:

• Me gusta revisar... = natural
• Yo me gusta revisar... = incorrect

You could add a mí for emphasis:

• A mí me gusta revisar cada diapositiva...

That would mean something like:

• As for me, I like to review each slide...
• or I personally like to review each slide...

But the basic sentence does not need yo.

Yes, that would be grammatical, but it changes the nuance slightly.

• cada diapositiva = each slide, one by one
• todas las diapositivas = all the slides as a whole

Also, the original antes de presentar nada en público means before presenting anything in public, which is broader than just before presenting in public.

So the original sentence suggests:

• before presenting anything publicly, I like to check each slide

Your alternative is possible, but it is not exactly the same in tone or meaning.

The given order is very natural:

• En julio y septiembre me gusta revisar cada diapositiva antes de presentar nada en público.

Spanish word order is somewhat flexible, but changing it usually affects emphasis.

For example:

• Me gusta revisar cada diapositiva en julio y septiembre...
  This pushes the time expression later.
• Cada diapositiva me gusta revisar...
  This sounds much more marked and less natural in everyday speech.

So while Spanish allows some movement, the original version is a good neutral order:

1. time expression
2. me gusta
3. infinitive phrase
4. time-related condition at the end