Looking to contribute for my roller coaster to make things better

I am wanting to build better roller coasters but how do I do it

That's way too broad a question. Basic things like the depumper, paying attention to the raduis comb, and paying attention to G-force readouts in play mode can go a long way.

And the flow on your layout must feel natural and not to forced.

I have broken parts of making a good coaster/park down into a few sections. I hope that this may help.

Creating a Realistic Ride

The best way to make a realistic coaster is to watch POVs and look at pictures of existing rides of the models that you are trying to build. For example, watching the POV of an existing Vekoma Minetrain. and then building one in NoLimits. I also recommend taking a look at some of the parks on the exchange for inspiration. However, something that can make coasters much more interesting is adding a few unique elements to the layout. Another way to practice making coasters is to recreate existing rides, even a simple ride like Thorpe Park's Stealth. It can help you get to know a manufacturer's style better. Use multiple elements in layouts to make them more diverse.

Smoothing and G-Force

The most important thing to smooth a track layout in NL2 is the Depump function. It reduces the sudden changes in the track's curvature to smooth the layout. I recommend depumping every section of a layout (besides straight sections), although it sometimes may not give you what you want (don't in that case). It can also help reduce G force. As Soko mentioned, use the radius comb to measure how smooth your track is. The lower the spike is, the smoother your layout is. Almost always keep G forces under 5G, and eliminate red force sections. Bank the track where necessary, and make sure that laterals are kept low. Make the curve wider if red G force cannot be eliminated. Also make sure that transitions from straight to curved track are smooth. I sometimes allow a few extra laterals to keep the banking consistent throughout the curve.

Supports

This is a hard section to explain, since each manufacturer has their own style of supports. There are some YouTube tutorials for this. Recreating a ride may also help you get to know a manufacturer's support style. Add supports frequently, and never give more than 20 feet without supports.

Hope this helps,
RMC It

I think of coaster design as both an art and a science. There are limits to what the human body can handle for G-force - and then there are limits for what will be comfortable to riders.

On the science side:

I like to cap most of my rides at about 4 G's positive (on rare occasion I'll approach 5 - but I'd say 5 is a hard limit, 4 is a good restraint and more comfortable - plus if you go slightly over 4 you're still fine). I'd say keep negative G's to about -1 G but occasionally you can spike at -1.3 or even -1.5 (and I'm sure some Sky Rush fans will disagree with me, but I don't like to exceed -1.5).
Laterals depend on the ride - big fast coasters usually keep laterals low. Ideally you won't ever go past 1 lateral G but wild mouse coasters can get more (I think of laterals like negatives - I cap at 1 for most rides, but occasionally go to 1.3 or even 1.5 depending on the ride).

It's also a good idea to build final brake zones and stations first before the rest of the layout. I like to get transfer tracks for maintenance in early - makes the whole build so much easier because transfer tables and maintenance bays take up a good bit of space. I like to build or at least have a good amount of space specifically set aside for my final brake run - even though often I don't know what the final speed of the ride will be, it's always good to just leave some room ahead of time.

Also - every coaster has block segments - any segment of track the train can come to a complete stop and then resume motion. LABEL YOUR BLOCKS. This will make your life so much easier. I like to use Disney's method and just name them "Zone 1" "Zone 2" etc... starting with the first block and then work my way around the track. I personally name my maintenance bays "Bay 1" and "Bay 2" and so on - but use a system that makes sense to you and helps you understand your track layout.

With brake runs - if you don't have drive tires or magnets, slope them. Easy to remember but this has been forgotten on even real rides (looking at you Space Mountain WDW).

Finally - build for people. Your station and queue need room. I have a guide on building codes on the forums, but it's very technical so I won't post it here. Just be sure to walk around in first person mode to get a sense of your space when it comes to queues and stations - that's a good start and you can dive into more technical stuff later.

For the art side:
Rides not only need to be fun to ride, they should be aesthetically pleasing. Good coaster design also involves a good choice of color scheme, a good vehicle choice, and using buildings and terrain to your advantage. I always like to incorporate iconic photogenic moments to my track layouts - it's great for advertising your ride too.

As with any art form, like others have said, study existing artists. Spend a day and just watch Vekoma ride POVs - get a sense of their style, what maneuvers do they use on their different ride systems - are banking transitions similar on mine trains as they are on their mega coasters?
Do they heart-line? If so, by how much?
Pay attention to the little details - where do lift chains start and stop? How long are brake runs and how quick do trains stop?
How do they do their maintenance bays?
Spend a day with the other manufacturers doing the same - anything from B&Ms to Intamins, to Mack coasters, RMCs, you name it.

Once you learn the conventions of style - THEN you can break the rules.
But learn the rules FIRST - you can't innovate and explore your personal style until you understand the basics.

Don't try to force your own style - that will happen naturally over time as you make more rides and try to replicate real manufacturer's styles. Personal style tends to arise organically so don't worry about it and just go with the flow as you design.

I definitely agree with RMC It's recommendation to build recreations - they challenge you and help you learn coaster design better.

Above all else: practice, practice, practice.

Your first coasters aren't going to be the greatest rides ever made. That's ok. Just keep building coaster after coaster after coaster. It really is an input/output machine like any other skill - the more time and practice you put in, the more you will get out. You can't rush it.

I've been designing coasters for well over a decade in several softwares and I still learn new tricks and ideas all the time - so never stop learning.
Don't beat yourself up if you made a ride and it's not that great - even the greatest artists have a giant catalog of scrapped projects behind every successful design.

So get out there, learn what you can, and build as many coasters as you possibly can.

Happy building man.
-Coastin' Dave