Nowadays its not that easy. Two out of three 'recruiters" out there are really resume hunters, also called resume farmers. They get paid for each resume they collect, then take your resume and shotgun it out to dozens of companies. Its a cheap and lazy way for them to make a living while screwing you over. They quicker and more often they ask for your resume, the more likely you will never hear from them again after you send it.
While this might sound nice, what happens if a company gets the same resume from more than one source? In theory, they are supposed to go with who sent it first. In reality they discard the candidate to avoid the hassle of recruiters battling over commission. For this reason alone you should be very careful who you send your resume to.
I was once contacted by multiple recruiters for the same job in Silicon Valley. Each gave me the same spiel, I was perfect, yada yada yada. In each case after I sent the recruiter my resume, they stopped all communications. I have since wised up.
NEVER NEVER NEVER send a resume to anyone that is a consultant - a recruiting consultant is a resume farmer, period.
Remember that a recruiter makes money off one of the most important decisions in your life - selecting a job. Never immediately trust that person. Be friendly, get them on the phone and make sure they understand they job they claim to be placing you for. A sincere recruiter will understand the company, the culture, and a bit of the internal politics. If their understanding of the company is limited to what's written in the job description and if they use the same language as the job description, don't trust them.
Make sure the recruiter speaks your language fluently. A large company will have their pick of recruiting firms just like a bikini model has her pick of suitors. Its unlikely an English-speaking HR professional for a large highly profitable company will sign an expensive recruiting contract with people they can't understand, and neither should you.
First refer them to your LinkedIn profile. Then verify they are where they say you are. I've been emailed by recruiters with a California phone number and address, but when I send them an email with a tracking pixel it turns out they are in India or the Philippines. Run away fast from them if they lie about their location. Trust me, IBM will not use a recruiting firm based in Russia.
Get them on the phone, see what they actually know about the company. Don't be fooled by "I talked to the hiring manager and he likes you". REAL RECRUITERS KNOW THEIR CLIENTS! Ask who their client company recently hired or fired, any recruiter worth the price of a cup of coffee will know that and that should convince you.