Choosing a dildo comes down to four things: material, size, shape, and whether you want it to do anything besides be there. Sort those and you will end up with something you actually reach for, rather than something that lives at the back of a drawer. Most of the regret people have about a first dildo traces back to skipping one of the four.
Material first, always
Body-safe means non-porous, and for dildos that almost always means silicone, glass, or stainless steel. Silicone is the most popular for good reason: it warms to body temperature, has a little give, and comes in every shape going. Glass and steel are firmer, hold temperature (warm or cool them first if you like that), and are effortless to clean.
Avoid porous "jelly" and unspecified materials. They can harbour bacteria and sometimes contain softeners you would rather not have against internal skin. A silicone dildo like the SilexD range gives you a realistic feel in a body-safe material, which is the combination that used to be hard to find.
Size: smaller than you think
A common first mistake is going too big. Screen size looks impressive and translates poorly to how a body actually feels. For a first dildo, check the insertable length and girth on the product page and choose what sounds comfortable rather than impressive - modest dimensions leave you room to learn what you actually enjoy. You can always size up later once you know what you enjoy; sizing down after an intimidating purchase is just a waste.
Girth matters more than length for most people, because it is what you feel most. Be honest about what is comfortable rather than aspirational. Comfort is what makes something get used.
Shape: curved, straight, or realistic
A gentle upward curve is worth considering because it is angled to reach the front vaginal wall, where the G-spot area sits - firm, targeted pressure there is what many people are after. A straight shaft is more versatile and often better if you also want to use it anally (with a flared base, always). Realistic shapes, with detailing and a defined head, are about the look and feel of the real thing; abstract shapes are purely about sensation. None is better; they are different preferences.
Features worth having
A few practical extras genuinely earn their place. A suction-cup base frees your hands and lets you use it against a surface. A flared base is non-negotiable for any anal use - it is the safety feature that stops a toy going where it should not. Harness-compatibility matters if you want to use it with a partner and a strap-on. And some dildos vibrate, which is a different experience again rather than simply "more".
Putting it together
For a confident first choice: silicone, a size on the modest side of what appeals, a slight curve if you want internal pressure or straight if you want versatility, and a flared or suction base so it earns its keep. That kind of shape suits a wide range of bodies and uses, which is exactly what you want while you are still learning your own preferences.
Pair whatever you choose with a good water-based lubricant - it makes everything more comfortable, and it is safe with silicone where silicone lube is not.
The short version
Body-safe material, sensible size, a shape that matches whether you want G-spot pressure or versatility, and a base that suits how you will use it. Get those four right and the rest is preference. Start a little smaller than instinct suggests, and let what you actually enjoy guide the next one.
The right size is the one that suits you now - you can always choose differently next time.