One of the best ways to set a goal is to use the SMART goal method.

S - SPECIFIC
The goal must be well defined and specific. Think of the 5 W's

Who
What
Where
Why
When
If your goal is to "get fit", what does that mean to you? Does "get fit" mean to look a certain way? To perform a certain way?

M - MEASURABLE
The goal must be able to be measured so that you know you are progressing.

If your goal is to "lose weight", how much do you want to lose?
A - ACHIEVABLE
The goal must be achievable. Think about the following questions:

Do I have the resources and capabilities to achieve the goal? If not, what am I missing?
Have others done it successfully before?
R - REALISTIC
Closely linked to achievable, the goal must be realistically achievable given the available resources and time. Think about the following questions:

Is the goal realistic and within reach?
Is the goal reachable given the time and resources?
Are you able to commit to achieving the goal?
T - TIME- ORIENTATED
The goal must be time orientated. If there are no time constraints, you will lose your sense of urgency and motivation to complete the goal. Lucky for you, the Challenge has an end date, and week 12 will be the best time constraint for your goal.

Write down your SMART goal and put it in a place where you will see it every day.

An example may be:

To weigh 70kg by the end of the challenge (9th of August)
To barbell deadlift 140kg by the 9th of August