Building a layout is a multi-year (unless you are
@Chris333 is days
) so don't rush things and have a clear vison to strive toward.
Things to consider in no apparent order.
1: Plan
everything for every step, i.e. track laying, structure and road placement, temporary bridges so you can run trains, DC or DCC?, turnout control methods, etc.
2: Focus on learning quality track laying. Make a diorama to practice on, include a switch, etc. DOING is better than WATCHING
3: Learn to solder and buy the right tools to do it.
4: Practice scenery concepts on foam scraps before doing it on your layout
5: Focus on the steps separately- Have a vision to follow, but work and think in steps
6: spend time looking at the progress of layouts
here. you will see others work and how they accomplished their goals and processes
7: be flexible to allow alterations to your original plans
8: Choose your scenic products, ballast, ground cover, trees, paints, etc.
9: Give your layout an identity and a vision or purpose, and consider creating a layout thread in the link above where you can share your trials and successes and gain valuable advice from experienced, and some famous creators (myself excluded).
Possible steps, I say possible because they can be in different order for different reasons, see 1 above.
A: build benchwork
B: transfer track plan to benchwork
C: terraform- thinking in 3D can sometimes alter your original plan. See 7 above
D: paint the foam in earth tones for your desired area, plan for structures and roads
E: lay track and fully wire, including fake bridges/trestles that will be replaced with your real ones, use a reliable method, see 1 above
F: Paint track, taping off turnouts to protect them
G: ground covers, i.e. dirt
H1: ballast track
H2: scenic ground cover grass, etc.
H3: Add roads; styrene for concrete, gravel for gravel roads, dirt for dirt roads, etc.
J: Lighting, circuits, products, etc.? See 1 above
Face this as well you may have to alter step order and application methods, see 7 above
Have fun! For so many years my layout was stagnant for fear of doing something wrong or in the wrong order. I literally forced myself to dive in and learn that it is NEVER complete, and that just doing little things a bit at a time get you there. My layout is such that I cannot really run trains (no loops, lots of switching) until it the layout is fully complete so there is always something preventing me from running.
ABOVE ALL, JFRTM (the creator of that acronym can explain if you don't already know).
Just my two pennies and I'm sure others will chime in.