Если ты опаздываешь, лучше сразу предупредить коллегу, а не молчать.

In Russian, the present tense of an imperfective verb is often used in if-clauses for general or repeated situations.

So Если ты опаздываешь literally looks like If you are being late / if you are late, but in real usage it can mean:

• If you’re late
• If you tend to be late
• If you’re going to be late
  depending on context

Here it sounds like practical advice: If you’re running late, it’s better to warn your colleague right away.

So the present tense here is completely normal.

This is about aspect.

• опаздывать = imperfective, focusing on the process or situation of being late
• опоздать = perfective, focusing on the completed result: to end up being late

In an if-clause like this, Russian often prefers the imperfective when talking about a general condition:

• Если ты опаздываешь... = If you’re late / if you’re running late

Using опоздаешь is possible in some contexts, but it would sound more like a specific future result:

• Если ты опоздаешь... = If you end up being late...

So опаздываешь is more natural for general advice.

Лучше + infinitive is a very common Russian structure meaning:

• it’s better to...
• you’d better...

So:

• лучше сразу предупредить коллегу = it’s better to warn your colleague right away

There is no verb like is in the Russian sentence. Russian often omits it in this kind of structure.

Common examples:

• Лучше подождать. = It’s better to wait.
• Лучше уйти сейчас. = It’s better to leave now.

Again, this is an aspect choice.

• предупреждать = imperfective, to be warning / to warn in general
• предупредить = perfective, to warn once, successfully, as a complete action

Here the speaker means a single concrete action:

• warn your colleague right away

That is why the perfective предупредить is natural.

After лучше, both aspects are sometimes possible, but the choice changes the nuance:

• лучше предупредить = better to warn once, actually do it
• лучше предупреждать = better to have the habit of warning / better to be warning in general

In this sentence, the one-time action is the point.

Сразу means:

• right away
• immediately
• at once

So:

• лучше сразу предупредить коллегу = it’s better to warn your colleague right away

Its position is natural here because it modifies the action предупредить.

Russian word order is flexible, so you may also see:

• лучше предупредить коллегу сразу

Both are understandable, but лучше сразу предупредить коллегу sounds very natural.

Because предупредить normally takes a direct object in the accusative case:

• предупредить кого? = to warn whom?

So:

• коллега = nominative
• коллегу = accusative singular

That is why the sentence has:

• предупредить коллегу = to warn a colleague / your colleague

You may also see a different pattern with extra information:

• предупредить коллегу о чём-то = to warn a colleague about something

But the person being warned still stays in the accusative.

Russian often omits possessives like my, your, his, etc. when the meaning is obvious from context.

So предупредить коллегу can naturally mean:

• warn your colleague
• warn the colleague
• warn a colleague

In English, you often need to choose one. In Russian, the noun alone is often enough.

If you wanted to make it explicit, you could say:

• предупредить своего коллегу = warn your colleague

But in this sentence, that would usually sound unnecessary.

Here а не is the natural choice because it sets up a contrast between two options:

• warn your colleague, rather than stay silent

So:

• лучше сразу предупредить коллегу, а не молчать
  = it’s better to warn your colleague right away instead of staying silent

А often means something like:

• whereas
• while
• rather than
• as opposed to

Using но here would sound less natural, because но is more like simple but, while а не clearly contrasts the preferred action with the rejected one.

Because it is paired with the other infinitive предупредить after лучше.

The structure is:

• лучше [do X], а не [do Y]

So both actions appear as infinitives:

• предупредить
• молчать

This is similar to English:

• It’s better to warn your colleague right away, not stay silent
• or more naturally, ...rather than stay silent

Not quite. In Russian, предупредить can mean:

• to warn
• to notify
• to let someone know in advance

In this sentence, it is probably closer to:

• let your colleague know
• inform your colleague
• give your colleague a heads-up

So although warn is a possible translation, the Russian verb can sound a bit broader and less dramatic than English warn sometimes does.

Because Если ты опаздываешь is a subordinate clause introduced by если (if), and Russian normally separates it from the main clause with a comma.

So the structure is:

• Если ты опаздываешь, = If you’re late,
• лучше сразу предупредить коллегу, а не молчать. = it’s better to warn your colleague right away rather than stay silent.

This comma is required in standard Russian spelling.

Yes.

• ты = singular informal you
• вы = plural you or singular formal you

So a more formal version would be:

• Если вы опаздываете, лучше сразу предупредить коллегу, а не молчать.

That would be appropriate when speaking politely to one person or addressing a group.

Yes, Russian word order is flexible, but different orders change emphasis.

The original:

• Если ты опаздываешь, лучше сразу предупредить коллегу, а не молчать.

Possible variations:

• Если ты опаздываешь, лучше предупредить коллегу сразу, а не молчать.
• Лучше сразу предупредить коллегу, если ты опаздываешь, а не молчать.

These are still understandable, but the original sounds smooth and natural because it presents:

1. the condition
2. the recommended action
3. the contrasting bad option

So it is a very standard and well-balanced word order.