Regarding claims, having claims that are "too broad" can also impact viability. Thus the concept of "limiting the claims" can be very important.
There is a somewhat recent trend, via pharma, that new uses for an existing method are patent eligible, which demonstrates the principle of limiting claims. (i.e. not seeking patent for the method in general, as applicable to any use, but claiming a specific use.)
See: Understanding Patent Claims and 35 U.S. Code § 112
Eligibility may also depend on the "field of the invention" 37 CFR 1.71 . [See also: Understanding the Specification of the Invention]
For instance, certain types of methods may be deemed too "abstract" by the patent reviewer, as in the case of some algorithmic patents. If the invention is for a physical device, either mechanical or computer hardware, the poorly defined term "abstract" won't likely be an issue.
Also understand that in patent law, nothing is certain, and the scope of what constitutes patent eligible subject matter is always changing.
Provisional Patent Applications
If you believe in your invention, but aren't quite ready to shell our a lot of money, definitely pursue a provisional patent. This gives you a year of "priority", and does not require public disclosure. You can use this to protect the IP if you plan on "shopping it" to investors, who are unlikely to sign non-disclosure agreements.
Many recommend attorneys, even for provisionals, but not all attorneys share this view. So long as the provisional is clearly written, supported by clear drawings and sufficiently explains how to make and use the invention, it can protect temporarily whatever is covered, so long as a formal patent application is subsequently submitted, and ultimately receives a grant. Provisional patent applications also carry the right to use "patent pending".
The key for provisionals is to be exhaustive. Anything you omit will not receive protection, and, even if subsequently filed, will not have the the same priority (date of submission of the original document).