Do not just send a random selection of poems. Periodicals that use poetry generally use poems that fit their focus. For example, a family magazine will want family-oriented poetry, a senior citizens magazine will use poetry related to nostalgia or aging issues, etc. If you carefully match your poetry to the appropriate markets, your chances of selling are much greater.
The reason you prepare poetry as separate manuscripts is so editors can select the poems they want and return the others. Also check the poetry sections to see what type of poetry an editor prefers. Some accept any type, while other may prefer rhymed or unrhymed. Send them what they want. Most periodicals pay little or nothing for poetry (although there are exceptions), but if you are a poet you want to get your poetry published everywhere you can whether you are paid or not. The good poets rise to the top eventually, but you will never be discovered unless you are published widely. It is the established poet who has the best opportunity of having a book of poetry accepted by a royalty publisher.
Poets often ask whether they should enter poetry contests or submit to poetry anthologies. Contests are a good way to get some recognition for your poetry as long as there are no or low entry fees. A poetry contest that charges high entry fees is likely in it for the money—not to discover promising poets. The same is true of anthologies. Some are legitimate, some are not. Never get involved with an anthology if you must buy one or more copies as a requirement for entering. Buying a copy should simply be an option, not a requirement. Also, try to find out if they accept everyone, or if they select only the best poetry. There is no value for you being included in an anthology that is filled with awful poetry.