Optimizing MySQL server -my.cnf

VPS Server Information Intel(R) Xeon(R) CPU E5-2620 0 @ 2.00GHz 5 GB ram What are the best settings for the server my.cnf file? Server speed is very low indeed. Few visitors to increase server load goes up to 7 to 15 My.cnf file settings are as follows : [PHP][mysqld] slow_query_log=1 long_query_time=0.1 long_query_time=10 #--slow-query-log-file=/var/lib/mysql/slow.log log-error="/var/lib/mysql/error.log" innodb_additional_mem_pool_size=512M innodb_buffer_pool_size=1000M innodb_file_per_table=1 #innodb_log_buffer_size=8M #innodb_flush_log_at_trx_commit=1 innodb_flush_method=O_DSYNC myisam_sort_buffer_size=64M #expire_logs_days=7 thread_cache_size=16 max_allowed_packet=32M skip-federated table_definition_cache=3000 local-infile=0 table_open_cache=5000 max_connections=100 max_user_connections=50 thread_concurrency=8 port=3306 query_cache_size=50M query_cache_limit=1M query_cache_type=1 socket="/var/lib/mysql/mysql.sock" skip-external-locking default-storage-engine=MyISAM open_files_limit=1500 tmp_table_size=30M max_heap_table_size=30M read_buffer=8M key_buffer=400M sort_buffer_size=256K read_buffer_size=2M join_buffer_size=512K key_buffer_size=500M [mysqldump] max_allowed_packet=16M quick [mysql] no-auto-rehash [mysqlhotcopy] interactive-timeout myisam_use_mmap=1 innodb_stats_on_metadata=0[/PHP]