I think it's important to begin with God's word because the Father has revealed his Son (Matthew 16:15-17), who is his Word (John 1:14), to his chosen people. Because he has revealed his Word to us, we can start there. Faith is the foundation of knowledge (Proverbs 1:7, Proverbs 9:10, Psalms 111:10). The root word of science is knowledge. The goal of science, then, is not to prove God, or deduce God, or test God. It is to gain knowledge. Gaining knowledge is a good thing - insomuch as it promotes wise dealing, righteousness, justice, and equity (Proverbs 1:3), and does not puff us up and cause us to act arrogantly, or cause others to sin (1 Corinthians 8:1-2).
So then, creation science
begins with belief in God, and reasons from there. But it must be remembered that this reasoning operates within the very limited confines of human understanding (Job 38:4). That said, creation science delves into speculation...
knowing that they're only speculating. For example:
Christian astrophysicists have proposed various explanations as to how God
might have created things in such a way that even Adam and Eve would have been able to see distant starlight.
Creation.com
They then go on to speculate, basing those speculations on evidence: possible explanations of distant starlight could be time dilation, or if light travels at a different speed when measured in one direction than when measured bouncing off something.
This type of thing may be cause for an accusation of pseudo-science. But it is important to remember that this is
admitted speculation: an educated guess, not a claim of knowledge. Furthermore, if science really means knowledge, and if it's really based on observation, then
any attempt to describe events prior to the existence of mankind is
not science - at least, not in the same sense that predicting the weather or improving a product or identifying a suspect is science. If there are no records of credible eyewitnesses describing an event, then it is by definition
unobserved. One can guess, one can deduce, one can build complex mathematical models to estimate, but none of this can be verified by direct observation.
So in some sense, the claim that creation science is pseudo-science is a claim that
any prehistoric science is pseudo-science. If you define science in such a way that it depends on direct observation, then you need to be consistent. But if you're willing to include educated guesses in what you want to call "science", then you need to include those educated guesses which are based on scriptural evidence at least as much as educated guesses based on other sources of information.
That is my non-expert approach. If you want the approach of people a little more knowledgeable than I, you could also look here:
Creation isn’t science?