Firstly,

The first step is

First of all,

The first stage is

To begin with,

... begins with

Initially

... commences with

Beforehand,

Before this,

Previously,

Prior to this,

Earlier,

At the same time,

During

Simultaneously,

When this happens

While

Secondly, Thirdly etc

After this,

Next,

The next step is

Then,

In the next stage,

Subsequently,

In the following stage,

Later,

Following this,

As soon as _______ has finished its work,

Eventually,

... until ...

Lastly

... finishes with ...

Finally,

concludes with

In the last stage,

The last step is ...